Wiki

There are many technical terms you might come across as you learn about repair, how things work, and electrical and electronic fundamentals, but don't let that put you off. Here you will find simple definitions of most of them.

Summary

The Restart Wiki tries to assume no previous knowledge, only a willingness to learn, and so we try to introduce and explain technical terms as we go along. But you might dip in and out or read the end of an article before the beginning, or you might consult other sources containing unfamiliar terms.

So this page gathers together as many technical terms as possible that you might come across in your fixing-related research, cross-referenced and linked in to main wiki articles where relevant.

You will find your favourite search engine or Wikipedia also to be valuable resources for looking up unfamiliar terms - those will often give you more detail.

Glossary of Terms

0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Term	Meaning
0 - 9
0-Day	See Zero Day.
2FA	See Two factor Authentication.
A
AC	AC or Alternating Current is an electrical supply which reverses direction many times per second. See AC and DC in the Wiki.
AC/DC motor	See Universal Motor.
Adware	Adware is a type of malware which presents you with unwanted advertising that you never knowingly agreed to receive.
AF	AF or Audio Frequency is a frequency within the audible range of approximately 20Hz - 20kHz.
Aftermarket	Aftermarket refers to spare parts, consumables or accessories for an item not manufactured and sold by the item's manufacturer, but by a third party.
AM	AM or Amplitude Modulation is a method of modulation in which the amplitude of an RF signal is modulated by the AF signal to be transmitted. See Amplitude Modulation in the Wiki.
AMD64	AMD64 is a 64 bit CPU architecture created by AMD as an evolutionary development of the Intel x86 32 bit architecture.
Amp (A)	The Amp is the unit of electric current, i.e. the quantity of electricity passing, a bit like the amount of water flowing in a river. Named after French mathematician and physicist André-Marie Ampère, remembered for his early work on electromagnetism. See Electric circuits, volts amps watts and ohms in the Wiki.
Analogue	Analogue is a method of representing a signal by a voltage (or a current) which is directly proportional to the value of the signal at any instant. For example, the output of a microphone is a voltage which continuously varies in direct proportion to the pressure of the incident sound wave.
Anode	An Anode is a positive electrode.
B
B7G	B7G was a 7-pin base used on miniature all-glass valves.
B9A	B9A was a 9-pin base used on miniature all-glass valves.
BC	BC or Bayonet Cap is a type of lamp base fitted with a push-and-twist action. There are several sizes but the 22mm diameter size is much the commonest. See Types of bulb in the Wiki.
Bimetallic Strip	A bimetallic strip consists of two strips of different metals fixed together. When heated up, one strip expands more than the other, causing the combined strip to bend away from the one which is expanding more. Often made into a snap action to create a switch which snaps open at a given temperature.
Binary	Binary is a number system using only the digits 0 and 1, well suited to computers as they can represent those digits by the on and off states of a switch.
BIOS	The BIOS or Basic Input/Output System was a program built in to PCs up until around 2011, which controled the PC prior to booting and initiated the boot process. (Newer computers use UEFI). See BIOS vs UEFI in the Wiki.
Bipolar Transistor	See junction transistor.
Bit	A bit or binary digit is the smallest unit of data, representing one of two values or states such as 1/0, or yes/no, or love Marmite/hate Marmite.
Bluetooth	Bluetooth is a personal area networking protocol allowing an individual's personal devices to communicate with one another.
Bot	A bot (short for Robot) is a computer which has been compromised in order to autonomously use its Internet connection for spreading spam or malware. Usually it will be one of many such computers comprising a "botnet", under the control of a "bot herder".
Brick	To "brick" a device is to render it completely useless, i.e. having as much functionality as a house brick. This can happen, for example, if the wrong type of firmware is accidentally loaded. "Unbricking" it can then be challenging if not virtually impossible.
Bridge Rectifier	A bridge rectifier consists of four diodes connected in a diamond shape. Applying AC to two opposite corners, you get DC out of the other two. See Linear Power Supplies in the Wiki.
Brush	A brush in an AC/DC motor consists of a small block of graphite, a pair of which feed the current to the rotor via the commutator. See DC and Universal (AC/DC) Motors in the Wiki.
Brushless Motor	An Electronically Commutated or Brushless motor is a type of DC motor which uses an electronic circuit to switch the current between several coils in order to keep the rotor turning, instead of using a commutator and brushes to perform this function. See DC and Universal (AC/DC) Motors in the Wiki.
Byte	A byte or octet is 8 bits, which can be used to represent a single letter, number or punctuation mark, or a number between 0 and 255, or anything else that can have up to 256 values.
C
Carrier	A carrier is a radio frequency signal which is modulated by an audio signal (for example) so that the audio can be transmitted by radio.
Capacitor	A capacitor is an electronic component which can store electric charge. Its capacitance (or its capacity for storing charge) is measured in Farads. An old-fashioned name for it is a condenser. See Capacitors in the Wiki.
Capacitance	Capacitance is the property of storing electric charge measured in Farads, which is the purpose of a capacitor.
Cathode	A cathode is a negative electrode.
CFL	See Compact Florescent Lamp.
Circuit	Electricity really hates piling up, so it will only flow if it can go all around a complete circuit and come back to where it started.
Circuit Diagram	A vacuum cleaner, for example, may contain several paths or "circuits" around which the current can flow, and a computer may contain a huge number. A circuit diagram is a picture of all those paths (or some of them) allowing you to see how the parts are connected together and hopefully understand how it works.
CLI	A CLI or Command Line Interface is a type of user interface in which the user types commands at a prompt. Also known as a Character User Interface or CUI (pronounced "coo-ee"). The acronym is also used in telephony to mean Calling Line Identity, i.e. the phone number initiating a call.
COB	COB or Chip On Board is a method of construction in which one or more bare semiconductor chips are mounted directly on a circuit board rather than encapsulated in individual packages. It is often used in mass produced items such as calculators in which the chip is covered by a blob of black resin, and more recently to mount many LED chips on a base to form a high power lamp, or on a thin strip to make a filament type of LED lamp.
Commutator	The commutator is the part of the rotor of an AC/DC motor which receives the current from the brushes. See DC and Universal (AC/DC) Motors in the Wiki.
Compact Florescent lamp	A CFL or Compact Florescent Lamp is a type of light bulb consisting of a florescent tube bent into a compact shape. More efficient than traditional filament lamps but still falling well short of newer LED lamps. See Types of bulb in the Wiki.
Conductor	A conductor is a material which conducts electricity. Metals and carbon are conductors.
Continuity	Continuity refers to an intentional low resistance electrical path between two points in a circuit. A continuity tester is a device which tests for continuity, often giving an audible beep when continuity is detected.
CPU	The CPU or Central Processing Unit is the "brains" of a computer which executes a computer program.
Crapware	Crapware is a somewhat vulgar term (best not used in polite company) referring to the largely useless junk software often bundled by a manufacturer with a Windows computer or an Android tablet or phone.
Crimp	A crimp is a type of connection where a wire is inserted into a tubular receptacle which is then crushed onto the wire with a special purpose crimping tool. Correctly formed, a crimped connection is generally stronger than a soldered one, and can be done faster and more reliably in a production environment.
CRT	A CRT or Cathode Ray Tube is the image-producing device in old fashioned televisions, computer monitors, radar sets and oscilloscopes. It consists of an evacuated glass enclosure in which electrons are fired at a fluorescent screen to create the image. Superseded by much less bulky LCD displays.
CUI	A Character User Interface or CUI is a user interface operated exclusively with a keyboard by typing commands at a prompt or selecting options from a menu. This is in contrast to a Graphical User Interface. Also known as a Command Line Interface or CLI.
Custom ROM	A custom ROM is an alternative to the operating system provided by the vendor for a device such as a smartphone.
D
DAB	DAB or Digital Audio Broadcasting is the standard used for digital broadcast radio.
DC	DC or Direct Current is an electrical supply which goes in one direction only. See AC and DC in the Wiki.
DDOS	A DDOS or Distributed Denial of Service attack is one launched via many different computers across the Internet, so increasing its power and making it harder to defend against.
Decimal	Decimal is the number system we commonly use in everyday life, based on the digits 0 - 9.
Desktop Manager	The Desktop Manager is that part of an operating system which represents the computer's applications and tools on the screen as items on a desk.
Diac	A DIAC is a 2-terminal electronic component which switches from a non-conducting to a conducting state when a certain voltage is applied, then remains conducting until the current is switched off. Commonly used in conjunction with a triac in dimmer switches.
Dielectric	A dielectric is an insulating material in which the positive and negative charges in the atoms or molecules can be displaced slightly in opposite directions from their natural positions by an electric field, causing the material as a whole to exhibit an electrical charge.
Digital	Digital is a method of representing, processing and transmitting a signal or a quantity as a number or sequence of numbers, usually expressed in binary as ones and zeros.
DIL	DIL or Dual In-Line is a type of IC packaging with 2 parallel rows of pins, designed for through-hole assembly.
Diode	A diode is a 2 terminal electronic component allowing a current to flow in one direction but not the other. See Diodes and Rectifiers in the Wiki.
Dipole	A dipole is a thing with two opposite ends, such as a magnet (with North and South poles), a molecule with a positive charge at one end and a negative charge at the other, or a type of aerial consisting of two rods placed end to end.
Distro	A distro is a flavour of Linux comprising a kernel, a desktop manager and a selection of utilities.
Demodulation	Demodulation is the process of recovering an audio or TV signal (for example) from the RF signal received from an aerial.
DLP	DLP or Digital Light Processing is a class of data projector using a Digital Micromirror Device to produce the image.
DMD	A DMD or Digital Micromirror Device is an imaging device containing a tiny electrically operated mirror to control the brightness of each pixel.
DMM	A DMM or Digital Multimeter is a Multimeter with digital readout.
DOA	DOA or Dead on Arrival refers to a brand new item which fails to work when first unboxed and switched on.
DOS	A DOS or Denial of Service attack is an attack which renders a service (such as a website) unusable for its proper purposes. See also DDOS. Also, a Microsoft operating system predating Windows, and lacking a graphical user interface.
E
Earth Loop	See Ground Loop.
E-Ink	A type of display, usually monochrome only, commonly used in e-book readers. It has the advantage of using very little power, and can be viewed by reflected ambient light rather than needing an active backlight.
EHT	Extremely High Tension. The name given to the very high voltage supply (usually in excess of 1,000V) required by cathode ray tubes in old fashioned televisions, magnetrons in microwave ovens and a few related devices. Needless to say, this can be very dangerous!
Electricity	Tamed magic. Well, mostly tamed.
Electrode	An electrical conductor making contact with a non-metallic part of a device such as a semiconductor or the electrolyte in a battery or the vacuum in a valve.
Electrolyte	A conducting liquid containing negative and positive ions, such as the liquid in a battery
Electrolytic Capacitor	A type of capacitor which employs an electro-chemical process to achieve a high level of capacitance. See Capacitors in the Wiki.
Electromagnet	A coil of wire wound around an iron core. A current passing through the coil magnetises the iron for only as long as the current flows. Typically used in electro-mechanical devices such as toasters, where it holds the lever down while the toast is toasting.
Electromagnetic Wave	(Often abbreviated to EM wave.) A kind of wave in space in which energy is continually exchanged between electric and magnetic fields in the same sort of way as energy in a ripple on a pond is continually exchanged between gravity and momentum. Radio waves, light, x-rays and gamma rays are all EM waves of different wavelengths.
Electron	A sub-atomic particle carrying a negative electrical charge. A flow of electrons constitutes an electric current.
Electronically Commutated Motor	See Brushless Motor.
EMF	Electro-Motive Force. Voltage.
Encryption	The process of transforming a message or data (the "cleartext") into a completely unintelligible form (the "ciphertext"). Only with knowledge of a secret key can the ciphertext be transformed back into the cleartext.
Epoxy	A type of very strong adhesive which comes as a resin and a separate hardener. It starts to set when the two are mixed together.
ES	Edison Screw. A screw-fitting lamp base. Several sizes are in common use. See Types of bulb in the Wiki.
ESD	Electrostatic Discharge. Static caused by friction such as shoes on a carpet, and particularly noticeable in conditions of low humidity. Even if not perceptible, it can damage sensitive electronic components.
Ethernet	A family of networking protocols defining several methods by which packets of data can be transmitted across a computer network.
F
Farad	The Farad is the unit of capacitance. Named after British scientist and experimenter Michael Faraday, who made important discoveries in the fields of electromagnetism and electrochemistry. See Capacitors in the Wiki.
Ferrite rod aerial	A type of aerial used for medium and long wave reception and consisting of a rod or block of ferrite (a magnetic but insulating material) with one or more coils of wire wound around it. See How radios work in the wiki.
Field Effect Transistor	A type of transistor where the current flowing between two of its terminals (the source and the drain) is controlled by an electric field created by a voltage on a third terminal (the gate). See Transistors in the Wiki.
FFC	Flat Flexible Cable. A type of cable with parallel conducting tracks on a plastic ribbon. Used extensively for connections between separate modules in a device.
Filament lamp	A type of light bulb containing a thin wire which glows white hot when a current is passed through it. See Types of bulb in the Wiki.
Filing System	That part of an operating system which manages a disk and presents it to the users as individual named files, without the users having to be concerned about where on disk their data is actually stored.
Firewall	A networking device which controls the traffic passing through it according to a defined policy, typically to prevent hackers from accessing a private network.
Firmware	Software which is built in to the hardware of a computer or smart device and is rarely if ever changed.
Flash	A term used for a type of memory that can only be changed by erasing and rewriting a substantial block of cells at a time. Flashing is used as a verb for the process of rewriting or updating such a memory.
Flux	A liquid or paste which helps to remove oxide or other deposits in order to make good solder joints. Only usually needed for challenging soldering jobs such as surface mount as solder normally contains a core of flux.
FM	Frequency Modulation. A method of modulation in which the frequency of an RF signal is modulated by the AF signal to be transmitted. See Frequency Modulation in the Wiki.
FPC	Flexible Printed Circuit. A flexible substrate with printed circuit tracks, generally brown or dark orange, and often having surface mount components or connectors soldered directly onto it.
Frequency	The number of complete (positive and negative) cycles of AC which occur per second. Measured in Hertz.
Full wave rectifier	A rectifier which uses both the positive and negative half cycles of the AC input to produce a DC output. Most often this is achieved with a bridge rectifier.
Fuse	A thin piece of low melting point wire designed to melt and so break the circuit if too much current flows due to a fault.
G
Germanium	A semiconductor used for the manufacture of early transistors but superseded by silicon and now mainly in solar cells and LEDs.
GB	Gigabyte: 1000 megabytes, but often used for 1024 megabytes, which is more properly written GiB.
GHz	A billion Hz
GiB	1,024MiB, or 1,073,741,825 bytes.
GPT	GUID Partition Table. The name given to a newer method of organising the contents of a disk. SeeMBR vs GPT disk layout in the wiki.
Grid	The control electrode in a valve. Driving it negative with respect to the cathode restricts or prevents a flow of electrons from the cathode to the anode.
Ground Loop	When two pieces of audio equipment are connected together, each having its own earth connection, some of the small current that should be going from one of the pieces of equipment to its own earth connection instead goes via the connection to the other equipment's earth, causing an objectionable hum in the audio output. This is known as a Ground or Earth Loop.
GUI	Graphical User Interface. Pronounced "goo-ey" A user interface operated principally using a graphical display and a mouse or other pointing device, as opposed to a Character User Interface.
GUID	Globally Unique Identifier. A 128 bit number used for identifying various types of resource in a computer system. A 128 bit number is so large that you can choose one at random and there is practically no chance that anyone else will ever pick the same one.
H
Half wave rectifier	A rectifier which uses only the positive (or the negative) half cycles of the AC input to produce a DC output, by using a single diode.
Hall Effect	When a current flows through a conductor and a magnetic field is applied to the conductor at right angles, the current tends to be pushed to one side of the conductor, at right angles to the magnetic field. This is the Hall Effect. Used in a Hall effect device to detect or measure a magnetic field, for example in smartphones to detect the earth's magnetic field to implement a compass.
Halogen Lamp	An improved form of filament lamp with longer life and better efficiency, but still far short of compact florescent and LED lamps. See Types of bulb in the Wiki.
Hard Disk	A hard disk or HD is a common type of computer main long term storage in which data is held on a rapidly spinning magnetic disk. (Increasingly, modern computers use a Solid State Disk instead.)
Hardware	The physical electronic and electromechanical parts which comprise a computer.
HD	See Hard Disk
Heat Sink	A piece of metal designed to conduct heat away from a component so as to prevent it getting too hot. When soldering, a pair of pliers can be applied to a lead of a sensitive electronic component as a heat sink to prevent the heat of the solder from damaging the component.
Henry	The Henry is the unit of inductance. Named after American scientist Joseph Henry, who made important discoveries in the field of electromagnetism (independantly of Michael Faraday). See Inductors in the Wiki.
Hertz	The Hertz (Hz) is the unit of frequency, numerically equal to cycles per second. Named after German physicist Heinrich Hertz, who was the first to prove the existence of previously theorised electromagnetic waves.
Hexadecimal	A number system based on only 16 digits which are represented by 0-9 and A - F. This is useful because each hexadecimal digit can represent 4 bits and 2 hexadecimal digits can represent 8 bits or a byte.
Hole	The lack of an electron in a crystal lattice where there should be one. This leaves behind a positive charge. An electron from an adjacent atom can move into the hole causing the hole to move to the adjacent atom. In this way, holes can act like positively charged particles and carry an electric current.
HT	High Tension. The name given to the main high voltage supply required by valve equipment, usually in the region of several hundred volts. Warning: this can be dangerous!
Hum	A constant low frequency sound in the output of audio equipment due (for example) to inadequate smoothing in the power supply and residual ripple in its output, or to the presence of a ground loop.
Hz	See Hertz.
I
IC	See Integrated Circuit.
IF	Intermediate Frequency. A frequency between the RF and AF in a superhet radio at which most of the amplification and selection of the required station occurs.
Impedance	For most practical purposes, the same as resistance, and also measured in ohms. Resistance is the number of steady volts you need to push a steady amp through a circuit, but if the voltage isn't steady or is AC, then inductance and capacitance add a kind of momentum and springiness to the way the current responds to the voltage, and then the volts per amp is termed impedance.
Inductance	The property of a coil of wire (or even a straight piece of wire) of storing energy in the form of a magnetic field generated by a current flowing through the wire. It is measured in Henrys. This energy is released back into the current, tending to keep it flowing, when the voltage driving it is reduced or withdrawn.
Induction motor	A type of electric motor, often used in fans, which runs only on AC. See Induction Motors in the Wiki.
Inductor	A coil of wire, very often wound around a magnetic core, providing a kind of momentum to the flow of electricity. Its inductance is measured in Henrys. See Inductors in the Wiki.
Inrush	A momentary surge of current drawn by a device on first switching it on, often causing a noticeable dimming of lights for a fraction of a second. Some equipment is fitted with a slow blow fuse to withstand the inrush. Items containing a large electric motor often have a significant inrush current as the motor starts.
Insulation displacement	A type of connection where insulated wire, without stripping the insulation, is forced into a slot with sharp inner edges. These edges cut through the insulation and bite into the wire. Commonly used on telephone and network connectors, and connectors deigned for attachment to ribbon cables.
Insulator	A material which doesn't conduct electricity, such as plastic, wood, glass and fresh air.
Integrated Circuit	An Integrated Circuit or IC is a circuit comprising anything from dozens to billions of electronic components, all fabricated on a single silicon chip. See Integrated Circuits in the Wiki.
International Octal	A type of 8-pin valve base used on older and larger valves, often referred to simply as "octal".
Internet	A global computer network in which, unlike the telephone network, information is transmitted as relatively small packets of data, each packet individually addressed and individually routed to its destination. Many different services use this foundation, two of the best known being email, and the World Wide Web, which delivers web pages.
Internet of Things	The Internet of Things (or IoT) refers to the networking of smart devices which have not traditionally been thought of as computers, such as vehicles, security cameras, home heating systems, kitchen appliances and medical devices, as well as industrial machines and sensors. As a result, they can be remotely monitored and controlled or can feed data back to a service provider, but if not properly secured (as is often the case) they can represent a serious security risk.
Intranet	A computer network using the same technology as the Internet but existing only within the confines of a particular company or organisation. However, most intranets have a gateway through which users can access the wider Internet, usually subject to certain restrictions.
Ion	A positively or negatively charged atom.
IoT	See Internet of Things.
IP	Internet Protocol. A set of standards defining how data (whether it be it web pages, emails or anything else), broken up into individually addressed packets, is moved across the Internet from a source to a destination. The Internet mainly uses Version 4 (IPv4) but the number of possible IPv4 addresses has been virtually exhausted. Version 6 (IPv6) provides a vastly increased number of addresses but has yet to see wide scale adoption on the Internet as a whole since interoperation is not straightforward.
J
Jack	The type of plug (and its socket) familiar as a headphone plug.
jFET	Junction Field Effect Transistor. A type of field effect transistor where the gate is formed by a semiconductor junction. See Transistors in the Wiki.
Joule	A measure of energy, being the amount of work done by 1 watt in 1 second. 4.2 Joules are equivalent to 1 calorie of heat.
Junction Transistor	A bipolar or junction transistor is a type of transistor with 3 semiconductor layers. See Transistors in the Wiki.
K
kB	Kilobyte: 1024 bytes.
Kernel	The core of an operating system, which concerns itself with managing the hardware resources at the lowest level. It normally has no user interface, this being provided by another program or programs referred to as the shell. Think of a nut. The shell is what you see but the goodness is inside in the kernel.
Keylogger	A type of malware which logs your keystrokes (including passwords, credit card numbers etc.) and sends them back to its creator, or stores them for him/her to collect later.
kHz	1,000 Hz
L
LAN	Local Area Network. A computer network covering a limited area such as a single building, or at most, a campus.
LCD	Liquid Crystal Display. The type of display used in most calculators, phones, tablets and computer monitors, which uses a special liquid which acts on polarised light under an electric field.
LDR	Light Dependant Resistor. A device having a high resistance in the dark but whose resistance falls with increasing illumination.
LED	Light Emitting Diode.
Linear Regulator	A circuit often in the form of an IC which produces a constant well defined voltage from a variable or poorly defined higher voltage input, simply by absorbing excess voltage and turning it into heat. See Linear Power Supplies in the Wiki.
Linux	A free, open source operating system kernel which, packaged into a distro, you can use as an alternative to Windows or OS/X.
Live Linux	A Linux system on a bootable CD/DVD or memory stick which can be run from that media without affecting the installed operating system on the hard disk.
Load cell	A device for measuring a force and presenting it as an electrical signal. See Digital weighing scales in the wiki.
Loupe	A magnifying glass, generally without a handle.
LT	Low Tension. The name given to the low voltage supply required by valve equipment to heat the cathodes of the valves. A common value is 6.3V.
M
Magnetron	The device which produces the microwaves in a microwave oven.
Malware	Any bad piece of software which attempts to get onto your computer for malicious purposes.
MB	Megabyte: 1000 kilobytes, but often used for 1024 kilobytes, which is more properly written MiB.
MBR	Master Boot Record. The name given to an older method of organising the contents of a disk. See MBR vs GPT disk layout in the wiki.
MHz	A million Hz
MiB	1,048,576 bytes.
Modem	A "modulator/demodulator" used to perform 2-way conversion of a data stream between digital and analogue forms, for example to communicate data over a voice or broadband (analogue) connection.
Modulation	The process of impressing an audio or TV signal (for example) onto an RF signal for transmission. See How radios work in the wiki.
MOSFET	Metal Oxide Field Effect Transistor. A type of field effect transistor where the gate is formed by metal deposited on an extremely thin insulating oxide layer. See Transistors in the Wiki.
MOV	Metal Oxide Varistor. The commonest type of varistor. See Varistor.
MTBF	Mean Time Between Failures. A measure of the reliability of an item, most usually measured in hours (or thousands of hours).
Multimeter	An electrical test instrument which measures voltage, current, resistance and often several other things. Most usually they have a digital readout but analogue ones with a dial are also available.
N
N-type	Semiconductor material doped with an impurity whose atoms have one too many electrons to match the crystal lattice, which can carry an electric current as negative charges.
NPN	A type of junction transistor comprising a P-type layer sandwiched between two N-type layers.
O
Object Code	Software in a form that can be directly executed by a computer, but is virtually unintelligible to humans, simply comprising binary numbers.
Octal	A number system based on only 8 digits 0 - 7. This is useful because each octal digit can represent 3 bits. See also International Octal (a type of valve base).
Octet	See Byte.
OEM	Original Equipment Manufacturer. A somewhat confusing term generally meaning a company which sells another company's manufactured goods under its own branding and with its own warranty. Also used of software, for a licence allowing a computer manufacturer to install the software on systems they build.(In fact, the manufacturer could be you, building a computer from standard parts.)
Ohm (Ω)	A bit like friction, the Ohm is the unit of resistance to flow of electricity. Named after German mathematician and physicist Georg Simon Ohm, chiefly remembered for discovering Ohm's Law. See Electric circuits, volts amps watts and ohms in the Wiki.
Ohm's Law	The amount of current (Amps) flowing in a circuit is the pressure (Volts) divided by the resistance (Ohms), or I = V / R.
OLED	Organic Light Emitting Diode. A light emitting diode using an organic (i.e. carbon-based chemical) semiconductor rather than one based on inorganic materials such as silicon or a compound of gallium. Also used to refer to a display made up of many OLEDs.
Open Circuit	Electricity likes to go all the way round a circuit and back to where it started. When there is a break in the circuit preventing the current from flowing (maybe due to a fault) this is termed an open circuit.
Open Source	Software or hardware the source code or design of which is non-proprietary and made freely available for anyone to inspect or modify for their own purposes.
Operating System	The software which manages the computing, storage and communications resources of a computer, and presents a user interface allowing the user to run and interact with programs as desired.
Opto coupler	An LED and a phototransistor, electrically isolated but in a single packaged. Used for signalling between two circuits which must have no electrical connection between them.
Oscillator	A circuit which produces an AC output at a chosen frequency.
Oscilloscope	A device for producing a graphical representation of how an electrical signal varies with time.
Own	In hacker parlance, to gain full control of a device or computer through subversive means. See also Pwn.
P
P-type	Semiconductor material doped with an impurity whose atoms have one too few electrons to match the crystal lattice. These result in holes which can effectively carry an electric current as positive charges.
PAN	Personal Area Network. A computer network linking a single person's devices, typically covering, at most, a single room.
Partition	A subdivision of a disk. Under the control of the operating system, a disk can be sliced up like a cake into several partitions, each partition being dedicated to a particular purpose. Otherwise, you would have to install another physical disk for each purpose.
Password Manager	A program or app which stores all your passwords in an encrypted vault under a (hopefully) strong master password. This makes it possible to use very strong totally random and unguessable passwords, which most password managers will generate for you.
PAT Test	Portable Appliance Test. This is a basic electrical safety test which should be applied to all mains operated electrical equipment before and after attempting a repair. It comprises a visual inspection and an automated test. See PAT testing in the Wiki.
PD	Potential Difference. A difference of voltage between two points in a circuit.
Peltier	A thermo-electric effect by which a junction between two different conductors or semiconductors warms if a current is passed through it in one direction and cools if it is passed in the opposite direction. The converse of the Seebeck effect. Used for cooling in mini fridges.
Pentode	A valve with 5 electrodes: an anode, a cathode and 3 grids.
Phillips	A type of cross-head screw or screwdriver, similar to but not quite the same as Pozidriv.
Phishing	The criminal practice of sending emails or messages through social media inviting the recipient to open a malicious attachment or visit a malicious website.
Photon	A particle of light.
Phototransistor	A light-sensitive transistor used for sensing light.
Piezo	The property of some materials to develop a voltage across two opposite faces when a physical force is applied, or to stretch or squeeze slightly if a voltage is applied. Pronounced "pee-ayzo" by some and "pee-zo" by others. The Oxford Dictionary allows either, but wars have been started over less contentious issues. Used in some microphones and earpieces, quartz crystal frequency standards, and gas lighters.
Pinout	A term used for the definition of the connections to each of the pins of a plug, a socket or an electronic component such as an integrated circuit with multiple connections.
PIR	Passive Infrared. A PIR detector detects heat radiation from warm bodies and is often used to turn on an outdoor security light, or to allow a room light to be turned off automatically when no one is there.
Pixel	An individual picture element, or coloured (or black and white) dot, thousands or millions of which make up a digital image.
PNP	A type of junction transistor comprising an N-type layer sandwiched between two P-type layers.
Pozidriv	A type of cross-head screw or screwdriver, similar to but not quite the same as Phillips.
Potentiometer (or Pot)	A resistor with a slider that can be moved along its length from one end to the other to tap off any required amount of resistance, for example for a volume control. Commonly known as a pot. See Potentiometer in the Wiki.
Power Supply	A PSU or Power Supply Unit is that part of a piece of equipment which takes the raw input power, for example from a battery or from the mains, conditions it, and delivers it at the voltage(s) the equipment needs internally.
PPE	Personal Protective Equipment. Equipment such as safety glasses, dust and fumes extractors, respirators, ear plugs, protective clothing etc. used for protection against health and safety hazards.
Primary Battery	A single-use battery.
PSU See #Power Supply.
PUP	Potentially Unwanted Program. Any useless but generally (though not necessarily) harmless program, often installed by the computer vendor, or (knowingly or unknowingly) installed along with downloaded software. The main purpose of it is usually to sell you some other software which you probably don't want.
PV Cell	Photo Voltaic Cell. A device for converting light into electricity, commonly known as a solar cell.
Pwn	In hacker parlance, to comprehensively "own" a device or computer. The term derives from a mis-typing of "own" in a video game in the 1990's.
Q
Qubit	A quantum bit which can be in two different states simultaneously. We have never seen one of these at a Restart Party, and if we ever do we will probably be undecided about what to do with it.
R
RAM	Random Access Memory. Very fast memory used by a computer as working store for data and programs currently being processed.
Ransomware	Malware which encrypts all your files then demands a ransom in order to recover them for you.
RAT	A type of Malware. A Remote Access Trojan allows a remote attacker to see your screen, to move and click your mouse and to type on your keyboard, just as if he were sitting in your chair.
Rectifier	A diode or 4 diodes connected together to convert AC to DC.
Reed switch	A sealed glass tube containing two magnetic contacts forming a switch. The switch can be closed by bringing a magnet near or by energising an electromagnet. It can be used as the switch in a reed relay or with a magnet attached to a moving part to detect when a cover is closed, a printer paper drawer is fully inserted, or a float in a tank is indicating the tank is full, etc.
Relay	A device consisting of a switch or bank of switches operated by an electromagnet. The switch(es) may be simple switch contacts or a reed switch.
Reservoir Capacitor	A large value capacitor used for smoothing rectified AC. See power supplies in the wiki.
Resistance	The property of resisting the flow of an electric current, measured in Ohms.
Resistor	An electronic component generally containing a thin metal or oxide film or a thin wire through which electricity flows with difficulty. It's resistance is measured in Ohms. A resistor always generates heat, even if only a tiny amount, and any replacement must be rated in Watts accordingly. See Resistors in the Wiki.
RF	Radio Frequency. A high frequency capable of being transmitted as a radio signal.
Ripple	Residual variation after smoothing in the voltage of a DC power supply at the frequency or twice the frequency of the AC mains input.
RJ11	A type of connector commonly used with telephones, with up to 4 connections and having a kind of barb which prevents it from accidentally being pulled out of a matching socket.
RJ45	A type of connector commonly used on network cables, with 8 connections and having a kind of barb which prevents it from accidentally being pulled out of a matching socket.
RMS	Root Mean Square. Since AC is continually varying it can't be measured as a unique voltage. The RMS value (a mathematical construct) is the DC voltage that would deliver the same power into a given load.
ROM	Read-only memory. Fixed memory which rarely needs to be changed, used for the most basic and lowest level functions in a computer.
Rootkit	An especially pernicious type of malware which subverts the operating system in order to expunge all references to itself and associated malware in listings of files and running programs etc., so as to mask its presence and hinder its removal.
Router	A network device connecting two or more networks. It forwards packets of data received from one network to its destination or to another router closer to its destination, on another network.
S
Sandbox	A kind of software "padded cell" in which untested or untrusted software can be tried out without risk to the host computer.
Schematic	Another name for a Circuit Diagram.
SCR	Silicon Controlled Rectifier. See Thyristor.
Secondary Battery	A rechargeable battery.
Sector	The smallest block of data a disk can read or write. On older disks this was normally 512 bytes but in modern disks and SSDs it is usually 4096 bytes.
Semiconductor	A material such as silicon, germanium or gallium arsenide which can be made to conduct electricity either by negatively charged electrons (N-type) or by positively charged holes (P-type), by adding small amounts of carefully chosen impurities.
SES	Small Edison Screw. A smaller version of the ES screw-fitting lamp base. See Types of bulb in the Wiki.
Seebeck	A thermo-electric effect by which a voltage is generated by a junction between two different conductors or semiconductors if it is heated or cooled relative to the rest of the circuit. The converse of the Peltier effect. Used by space craft venturing to the outer reaches of the solar system to generate electricity from a radioactive heat source such as a lump of plutonium.
Shell	A program which offers a user interface to lower level parts of an operating system (referred to as the kernel), which lack a user interface. The Mac or Linux command prompt is referred to as the shell, and the Windows Desktop is Windows' shell.
Short circuit	If two wires are touching which shouldn't the current may be able to take a short cut, meeting very little resistance and so allowing too much to flow. This is a Bad Thing and can cause things to get hot or even catch fire.
Shottky diode	A type of diode using a metal-semiconductor junction, mainly used in power supplies on account of its ability to operate efficiently at higher frequencies. See switching mode power supplies in the wiki.
SIL	Single In-Line. A type of packaging used for circuit sub-assemblies, resistor networks and some ICs with a single row of pins, designed for through-hole assembly.
Sine wave	The mathematically simplest form of vibration or oscillation, which can be represented by a single frequency only. Exemplified by the motion of a pendulum swinging through a small angle, or the height of a point on a wheel above or below the axle as the wheel turns at a constant speed.
S.M.A.R.T	Self-Monitoring, Analysis, and Reporting Technology. A technology built into all modern hard disks and solid state disks by which the device can monitor things like its error rate in order to report back and hopefully give early warning of impending failure.
Smoothing	The process of turning raw rectified AC, which drops to zero twice in every cycle of the AC, into a reasonably constant voltage. See Why is a power supply needed? in the Wiki.
Software	The step-by-step instructions which tell a computer what to do and how to do it.
Solder	A mixture (most often) of tin and copper or tin and lead with a relatively low melting point, making it very convenient for making electrical connections. (Americans call it "sodder", and many electrons have been harmed in discussions as to which is correct. But the Americans are on their own on this one.)
Solenoid	An inductor or electromagnet in cylindrical form.
Solid State Disk	A Solid State Disk (or SSD) is a faster (though more expensive) alternative to a hard disk for a computer's long term storage. A strange term in a way as it's no more solid than a hard disk, but a major difference (and advantage) is that it has no moving parts.
Source Code	Software in a human-readable form as created by a developer. Generally, this cannot be directly understood or run by a computer, but has to be translated into object code by a special program called a compiler.
Spam	Any unwanted email. This may simply be an irritation but often it will be a scam or contain malicious attachments or links.
Spear Phishing	A type of phishing attack directed at a specific victim who has probably been researched in order to make the attack seem highly plausible.
Spudger	A tool with a thin plastic or metal blade typically used (for example) for inserting into the crack between two halves of a plastic case in order to pry it open.
Spyware	A type of malware which reports browsing history and other personal information back to its creator without your permission.
SSD	See Solid State Disk.
Superhet	A common design of radio receiver in which the incoming signal, whatever its frequency, is converted into a fixed intermediate frequency to make it easier to tune and amplify. See Superhet in the Wiki.
Stepper Motor	A type of motor which, instead of turning continuously, turns by a certain fraction of a revolution and stops every time it is given an electrical pulse. Used, for example, for stepping the paper through a printer as it is being printed. See DC and Universal (AC/DC) Motors in the Wiki.
Surface Mount	A method of manufacture in which electronic components are soldered directly onto the surface of a printed circuit board, as opposed to the older through-hole method.
SWG	Standard Wire Guage. A set of wire diameters where each gauge is approximately 10% thinner than the previous, for example 16 gauge is 1/16in in diameter and 50 gauge is a thousanth of an inch. Cross sectional area in square millimeters is becoming a more usual measure. See Standard Wire Gauge in Wikipedia.
Switch-mode Regulator	A circuit which produces a constant well defined voltage from a variable or poorly defined voltage input, by switching the power on and off very rapidly and smoothing the result. See Switching Mode Power Supplies in the Wiki.
Synchronous motor	A type of electric motor which only runs on AC, and which runs at a speed which is locked to the AC supply frequency. See Synchronous Motors in the Wiki.
T
TB	Terabyte: 1000 gigabytes, but often used for 1024 gigabytes, which is more properly written TiB.
THD	Total Harmonic Distortion. A measure of the degree to which an audio system distorts its input, effectively introducing new frequencies into the output.
Thermal Paste	A paste with a special formulation making it a good conductor of heat, used to improve the transfer of heat from an electronic component to a heat sink.
Thermionic Valve	See Valve.
Thermistor	An electronic component like a resistor but with a resistance which decreases substantially with increasing temperature.
Through-hole	A method of manufacture in which electronic components are attached to a circuit board by passing their leads or pins through holes in the board and soldering them to the board on the other side, as opposed to the more modern surface mount technique which allows much higher component densities.
Thyristor	An electronic component with 3 leads used as a switch. Also known as a Silicon Controlled Rectifier. See Transistors in the Wiki.
TiB	1,024GiB, or 1,099,511,627,776 bytes.
Torque	A twisting force, such as applied by a screwdriver to a screw, a spanner to a nut, or produced by the spindle of an electric motor. It is measured in Newton Metres (Nm), being the twisting force created by a linear force of 1 Newton (102 grams weight on the earth) applied to a lever of length 1m, or twice the force applied to a lever of half the length etc.
Transducer	A device which transforms energy or a measurement from one form to another, e.g. sound to/from electricity (speakers and microphones), or temperature, light, force etc. to an electrical signal.
Transformer	Two (or more) coils of wire wound around a magnetic core, used to step a voltage up or down or provide isolation between two circuits. See Transformers in the Wiki.
Transistor	An electronic component with 3 leads used to amplify a signal or switch a current on or off. See Transistors in the Wiki.
Triac	A type of thyristor which, unlike the standard type, can be used on AC. Commonly used in dimmer switches.
TRIM	A means by which an operating system can tell an SSD about files that have been deleted. This is important for performance reasons related to the way an SSD works. See SSD Migration and Troubleshooting in the wiki.
Triode	A device with three electrodes. Most commonly used to denote a type of valve.
Trojan	A type of malware which hides inside legitimate software.
Torx	A type of security screw or screwdriver with a 6-pointed star shape.
Two Factor Authentication	Two Factor Authentication (2FA) is a login scheme where you are required to supply not only a password ("something you know") but also prove your possession of a token of some sort ("something you have") or provide a biometric such as a fingerprint ("something you are"). This makes it very much harder to compromise.
Tuned Circuit	A capacitor and an inductor connected together, which resonate at a particular frequency.
Two Step Authentication	A kind of "poor man's Two factor Authentication" where the second factor is a one time code delivered to you by text message. Whilst considerably better than a password on its own, this is no longer greatly recommended on account of the relative ease by which a determined criminal could get a SIM card registered to your phone number and so get hold of the one time code.
U
UEFI	Unified Extensible Firmware Interface. A program built in to newer PCs (since around 2011) which controls the PC prior to booting and initiates the boot process. (Older computers used BIOS). See BIOS vs UEFI in the Wiki.
Universal motor	An AC/DC or Universal motor is a type of electric motor that runs equally well on AC or DC. See DC and Universal (AC/DC) Motors in the Wiki.
V
Vacuum Tube	See Valve.
Valve	A thermionic valve or vacuum tube is an amplifying device consisting of a glass tube containing several electrodes in a vacuum. An electrically heated cathode emits electrons which are attracted by an anode. Their flow is controlled by the voltage on a wire mesh grid in their path. Long since superseded by much smaller and less power-hungry transistors in all but a few niche applications.
Varistor	A device which has a very high resistance until a certain voltage is reached, whereupon its resistance falls sharply. Used for absorbing transient voltage surges in a mains supply.
VDR	Voltage Dependant Resistor. See Varistor.
Virus	A term commonly used for any type of malware, but strictly meaning self-replicating malware.
Volt (V)	The Volt is the unit of electrical pressure, a bit like water pressure. Named after Italian physicist and chemist Alessandro Volta who is credited with the invention of the battery. See Electric circuits, volts amps watts and ohms in the Wiki.
Vulnerability	A flaw in a website or software product by which it can be compromised for malicious purposes, such as spreading malware.
W
WAN	Wide Area Network. A computer network spanning a substantial geographical area
Watts (W)	The Watt is the unit of power, calculated by multiplying the Volts by the Amps. Named after Scottish inventor, mechanical engineer and chemist James Watt, who invented the first truly practical steam engine. See Electric circuits, volts amps watts and ohms in the Wiki.
Wavelength	The distance between successive crests of a radio wave as it travels through the air. See Freqvency vs wavelength in the Wiki.
WiFi	A family of wireless local area networking protocols, allowing a number of computers and other devices within a reasonably confined space to talk to each other.
Worm	A type of malware able to spread across a network, or the whole Internet.
X
XP	An obsolete Windows operating system first released in 2001. Extended support ended in 2014 and remaining users are strongly advised to migrate to a supported operating system as security patches are no longer provided.
x86	The Intel CPU architecture derived originally from the 8086 chip, released in 1978. Subsequent generations were the 80286 (often referred to simply as 286), 386, 486 and 586 also known as Pentium. From 386 on, these were all 32 bit architectures.
Y
Yagi	A type of aerial commonly used for terrestrial television reception, and consisting of an array of parallel rods, the array pointing in the direction of the transmitter.
Z
Zener diode	A type of diode which starts conducting in the reverse (normally non-conducting) direction at a well defined voltage, often used in electronic circuits to define a threshold or specific voltage.
Zero Day	A vulnerability that is discovered (and very often exploited) before any fix is available, giving potential victims no time at all (zero days) in which to protect themselves. Also known as an 0-Day (pronounced "oh-day").