Glossary

Web words in plain English. Each one has its own short page with an everyday comparison and the lesson where you can try it.

Algorithm: A list of exact steps a computer follows to do a job, such as sorting a list or choosing which videos to show you. More →
Atomic clock: An extremely precise clock that keeps time by counting the vibrations of atoms. GPS satellites carry several. More →
Biometrics: Using a part of your body, like your face or fingerprint, to prove who you are. More →
Bot: A program that does a job automatically, such as playing a game, filling in forms or visiting websites, often pretending to be a person. More →
Browser: The app you use to visit websites. It fetches pages and draws them. More →
Cache: A store of answers kept nearby so they don't have to be worked out or fetched again. More →
ETag: A fingerprint of a file the server sends so a browser can ask later whether that exact copy has changed. More →
Cache-Control: An HTTP header that tells browsers and other caches how long a saved copy may be reused without checking again. More →
Checksum: A small number worked out from a piece of data. Work it out again later: if the numbers differ, the data got damaged. More →
Certificate: A digital ID card that proves a website is who it says it is. Your browser checks it before showing the padlock. More →
Client: Your device and the app on it, the side that asks a server for things. Servers check what clients tell them instead of simply believing it. More →
Cookie: A small note a website asks your browser to keep and send back on later visits. Useful for logins; also used for tracking. This site sets none. More →
Crawler: A bot that reads web pages one after another by following their links, so a search engine can note what each page says. More →
Decibel (dB): A way of measuring how much stronger or weaker a signal is. Losing 3 dB halves it; losing 10 dB leaves a tenth. More →
Domain name: The name part of a web address, like example.com, that a person or company owns. In a link, the owner is the part just before the first single slash. More →
DNS: Domain Name System: the internet's phone book, turning names into IP addresses. More →
Encryption: Scrambling information so only someone with the right key can unscramble it. More →
End-to-end encryption: Locking a message on the sender's device so that only the receiver's device can unlock it, with nobody in between able to read it. More →
File system: The part of a computer that keeps the list of which blocks on a disk belong to which file. More →
Fragment: The part of a URL after #. It stays in your browser and is never sent to the server. More →
Geostationary satellite: A satellite about 35,786 km above the equator that circles once a day, so it seems to hang still in the sky. More →
GPS: Global Positioning System: about 31 satellites that broadcast the exact time, so a receiver can work out where it is. More →
Hash: A fixed-length fingerprint of some data. One-way: you can't get the data back from it. More →
HTML: The language web pages are written in: headings, paragraphs, links and so on. More →
HTTP / HTTPS: The way browsers and servers talk. HTTPS is the encrypted version. More →
Infrared: Light just beyond red that our eyes can't see. TV remotes and face unlock cameras use it. More →
IP address: The number that identifies a computer on the internet, like 192.0.2.10. More →
Latency: How long a message takes to get somewhere and back. Measured in milliseconds. More →
Load balancer: A traffic controller that spreads requests across several servers. More →
Low Earth orbit: Space close to Earth, a few hundred to about 2,000 km up. Newer internet satellites fly here to cut the delay. More →
Mesh Wi-Fi: Several Wi-Fi boxes around a home that pass the signal between them, so far rooms get a strong signal too. More →
Overwrite: Saving new data on top of old data, which finally destroys what was there before. More →
Packet: A small numbered piece of a bigger message. Packets travel separately and are put back together at the other end. More →
Phishing: A fake message dressed up as someone you trust, sent to trick you into clicking a link or handing over a password, code or card. More →
Port: A numbered 'door' on a computer. Web traffic normally uses 443 (HTTPS) or 80 (HTTP). More →
Prediction: When your device guesses the next moment of a game before the server's reply arrives, so it feels instant. More →
Processor: The chip that does a computer's thinking, also called the CPU. It is made of billions of tiny switches, and all that switching makes heat. More →
Radio wave: An invisible wave of energy that travels at the speed of light. Wi-Fi, mobile phones and FM radio all use them. More →
Recommendation system: A program that scores lots of things (videos, songs, products) for each person and shows the top few, based on what they and similar people did. More →
Recycle bin: A holding area for deleted files so you can change your mind. Nothing is erased until it is emptied. More →
RAM: A computer's working memory: very fast, holds what programs are using right now, and goes blank when the power goes off. More →
Rate limit: A rule that slows down anyone making too many requests, to keep a service healthy for everyone. More →
Request / response: The browser's question and the server's answer. Every page load is a bunch of these. More →
robots.txt: A small text file at the top of a website that tells robots which parts they should stay out of. Good bots obey it; it isn't a lock. More →
Router: The box that connects your home to the internet and makes the Wi-Fi signal for your devices. More →
Salt: A few random characters mixed into a password before it is fingerprinted, different for every person, so identical passwords look different. More →
Server: A computer that waits for requests and answers them. This site runs on one with a single processor. More →
Status code: The three-digit number at the start of every response, such as 200 or 404. More →
Tick: One beat of a shared game world: the server updates positions and scores this many times a second. More →
Thermal throttling: When a gadget slows its chip down on purpose because it is getting too hot, so it makes less heat and cools off. More →
TLS: Transport Layer Security: the technology behind the padlock that encrypts web traffic. More →
Trilateration: Working out where something is from its distances to a few known points, where the circles (or spheres) around them meet. More →
TRIM: A message a computer sends to an SSD saying which blocks are free, so the drive can erase them in the background. More →
Tunnel: A connection the server makes outwards to a helper network, so visitors can reach it without any open doors on the server itself. More →
Third-party cookie: A cookie from a company other than the website you are on, such as an advert tucked inside the page. It can link your visits across many websites, so many browsers block it. More →
Two-step verification: A second check after your password, such as a short code from your phone that changes every few seconds. More →
Undersea cable: A cable on the sea floor holding thin glass fibres that carry data between continents as flashes of light. More →
Unicode: The worldwide list that gives every letter, symbol and emoji its own number, so all computers agree on what was typed. More →
URL: A web address, such as https://example.com/page. More →
UTF-8: The most common way to pack Unicode numbers into bytes: 1 byte for plain English letters, up to 4 for an emoji. More →
Zero-width character: A Unicode character that draws nothing on the screen but still counts in the text, such as a zero-width space or the glue inside some emojis. More →
Non-breaking space: A space that looks ordinary but uses a different number (U+00A0), so computers treat it as different from a normal space and usually will not wrap a line there. More →
Bitrate: How many bits a stream sends each second. A lower bitrate means a video call must use bigger blocks, fewer pictures, or freeze. More →
Compression: Squeezing data so it takes fewer bits: a video call describes patterns and changes instead of every pixel, so it fits a thinner pipe. More →
Byte range: A numbered slice of a file, named by start and end byte, so a download can ask for only the missing piece. More →
Partial content: HTTP status 206: the server is sending only the byte range you asked for, not the whole file. More →
Sync: Short for synchronise: devices swap their changes so every copy ends up the same. More →
Merge conflict: When two people changed the very same thing at once, so a rule or a person has to decide which change to keep. More →
Spam filter: A program that sorts junk messages and sometimes cleans risky markup; it usually moves whole messages, not single emojis. More →
Autocorrect: Software that rewrites what you type — fixing spelling, and sometimes turning an emoji into a plain word. More →
Substitute day: A weekday off given in place of a public holiday that falls on a weekend, so the day off isn't lost. More →
Statutory holiday: A day that employment rules treat as a paid day off. It is not the same as a day painted red on a calendar, or a day when school is closed. More →
Calendar feed: A calendar file (usually iCalendar, .ics) at a web address that apps download again regularly to stay up to date. More →
Polling: Asking again and again on a timer whether anything has changed, like checking the letterbox every hour. More →
Push notification: A message a website or app sends to your device the moment something happens, so the device doesn't have to keep asking. More →
Authorization: Deciding what someone is allowed to do once you know who they are, checked again on every request. More →
Revoke: To cancel access you gave earlier, such as a share link or a badge, so the next visit is refused. More →
Webhook: A web address one server gives another so it can be called the moment something happens, instead of checking over and over. More →
Metadata: Information about a file rather than its contents, such as when a photo was taken, on what phone, and sometimes where. More →
EXIF: The hidden notes a camera or phone writes inside a photo: date, camera, which way up, and sometimes the GPS location. More →
HEIC: The photo format many phones save by default; it looks like a JPEG at about half the size, but not every website accepts it. More →
Pixel: One tiny coloured square in a digital picture or screen; 12 megapixels means about 12 million of them. More →
Resolution: How many pixels a picture or screen has, such as 1920 by 1080; more pixels can show finer detail. More →
Pixelation: Turning part of a picture into big single-colour squares; it looks hidden but is not a safe way to hide text. More →
Redaction: Removing private parts of a picture or document so they are really gone from the file, not just covered up. More →
Upscaling: Making a small picture bigger by smoothing or guessing new pixels; it can't bring back detail that was lost. More →
Lossless compression: Packing that shrinks a file and can unpack the exact original, like a zip file. More →
Lossy compression: Packing that throws away some detail on purpose so the file gets smaller, like a JPEG photo or a blurry video call. More →
DHCP: The helper in your router that lends each device an IP address when it joins the network. More →
Port forwarding: A permanent rule on a router that sends anything arriving on one port number to one device at home, even if nobody inside asked for it. More →
NAT: How a router lets every device at home share one public internet address, swapping addresses on the way out and back. More →
MAC address: The name built into a network adapter, like 3C:22:FB:9A:41:0E; it is only used inside your own network. More →
QR code: A square black-and-white pattern a camera can read, usually holding a web address; check where it goes before opening it. More →
Error correction: Spare data worked out from a message so that missing or damaged pieces can be rebuilt, like the extra squares that let a scratched QR code still scan. More →
Quishing: Phishing with a QR code: a fake code, often a sticker over a real one, that leads to a page asking you to pay or log in. More →
Gateway: The door out of your home network, usually your router; anything not meant for a device at home is sent to it. More →
Subnet: A group of addresses that count as one neighbourhood, like every 192.168.1.something at home; devices in it talk directly. More →
Bandwidth: The most data a connection can carry each second, like the number of lanes on a road; internet plans are sold by it in Mbps. More →
Throughput: How much data actually gets through right now, usually less than the bandwidth because of Wi-Fi, walls and other users. More →
Roaming: When a phone or laptop hops from one Wi-Fi base station to another as you move around, without picking a new network. More →
Wi-Fi channel: One lane of the radio band that a Wi-Fi network uses; nearby networks on lanes that overlap get in each other's way. More →
Jitter: How much the waiting time wobbles from one message to the next; big wobbles make calls choppy and games jumpy. More →
Packet loss: When some of the small pieces a message is cut into never arrive, causing gaps in calls and players snapping back in games. More →
Bufferbloat: Lag caused by a router queueing too much data when the line is full, so small game and call messages wait behind big downloads. More →
DSCP: A small label inside each internet parcel that can ask for special treatment, such as a quick lane for calls; anyone can set it, so most networks ignore or wipe it. More →
Lithium-ion battery: The rechargeable battery in phones, tablets, laptops and electric cars, where lithium ions swim from one side to the other through a jelly as it works. More →
Internal resistance: How hard it is for electricity to get through a battery itself; it rises in the cold and as batteries age, so the voltage sags under heavy use. More →
Battery gauge: The little chip that works out a device's battery percentage by counting charge in and out and watching the voltage. More →
Watt-hour (Wh): A measure of how much energy a battery holds; unlike mAh it means the same thing for every battery, so it's the fair way to compare a power bank with a phone. More →
Milliamp-hour (mAh): The battery-size number printed on phones and power banks; it counts charge, not energy, so it only compares fairly between batteries at the same voltage. More →
USB Power Delivery (PD): The USB-C fast-charging rulebook: the charger and the gadget talk over the cable and agree a voltage and power, from 5 V up to 240 W. More →
Adaptive bitrate streaming: How video apps keep a film at several sizes and switch between them chunk by chunk to match your connection, so it starts quickly and rarely freezes. More →
Audio fingerprint: A tiny summary of a recording made from pairs of its loudest notes and the gaps between them, used to recognise a song from a few seconds of sound. More →
Spectrogram: A picture of sound with time across, pitch up the side and loudness as brightness, so a tune shows up as bright lines. More →
Video buffer: Video a player has already downloaded but not shown yet, kept in hand so the picture keeps going when the connection wobbles. More →
Infrared remote code: The pattern of invisible flashes a TV remote sends for each button: a wake-up flash, then bits shown by long and short gaps, with a flipped copy as a check. More →
Codec: The recipe a device uses to squeeze video or sound into a small file and unpack it to play, such as H.264, HEVC or AV1. More →
Frame rate: How many still pictures a video shows each second (fps). More frames look smoother but take more space. More →
Bluetooth: Short-range, low-power radio that gadgets use to find and talk to each other, like phones to headphones, or two phones finding each other before sharing a photo. More →
Wi-Fi: A way of joining the internet without a cable, using radio waves between a router and your devices, usually at 2.4 or 5 GHz. More →
Compression artefact: The blocks, smudges and fuzzy halos you see when a picture or video has been squished too hard and detail was thrown away. More →
MTP (Media Transfer Protocol): How an Android phone shares its files over a USB cable: the computer asks for each file and the phone fetches it, instead of handing over the whole storage like a USB stick. More →
exFAT: A file system for memory cards and USB sticks that Windows, Macs, cameras and TVs can all read and write, with no 4 GB file limit but no safety journal either. More →
Keyframe: A complete picture saved every so often inside a video, with the pictures in between stored only as the changes since. More →
Bottleneck: The slowest part of a chain of steps, which sets the speed of the whole thing however fast the other parts are. More →
SLC cache: A small, fast part of a USB stick's or SSD's memory that new data is written to first, so copies start quickly and slow down once it fills. More →
Journaling: When a file system writes a quick note of what it's about to change before changing it, so it can tidy up after a sudden power cut. More →
Partition table (MBR vs GPT): The small map at the start of a drive that says where each section begins; MBR is the old kind many cars and TVs need, GPT the newer one computers use. More →
SMART (drive health): The health logbook a hard drive or SSD keeps about itself, counting worn-out spots, read retries, temperature and wear, so tools can warn you before it fails. More →
SMS (text message): A short plain text sent through the phone network rather than the internet, up to 160 plain letters per text, passed from tower to message centre to tower. More →
Polling rate: How many times a second a controller, mouse or keyboard sends a fresh report of its buttons and sticks, such as 125, 250 or 1,000 times (Hz). More →
Input lag: The delay between pressing a button and seeing the result on screen, made of the controller, the connection, the game's frames and the screen added together. More →
Refresh rate: How many times a second a screen redraws its picture, such as 60, 120 or 144 times (Hz); more redraws look smoother if the game keeps up. More →
VRR (variable refresh rate): When the screen waits for each new picture from the game and redraws right then, instead of on a fixed beat, so there is no tearing or stutter. More →
Contention ratio: How much bigger all the homes' plans added together are than the shared pipe they use, such as 1:20. It works because people rarely use their whole connection at once. More →
CDN (content delivery network): Copies of popular films, games and web pages kept in buildings close to you, often inside your internet provider's network, so they don't have to travel from far away. More →
Store and forward: Passing a message on by keeping a copy at each stop and sending it to the next one only when that next step is ready, so nothing is lost if the far end is away. More →
Slow start: How a new internet connection begins with a small burst of data and doubles it every round trip until something is lost or the pipe is full. More →
HDR (high dynamic range): A way of describing pictures with much brighter highlights, deeper shadows and more colours than ordinary video; the screen then squeezes it into what it can actually show. More →
Fake-capacity drive: A USB stick or memory card whose controller has been set to report far more space than it really has, so files past the real size are lost or overwrite older ones. More →
Thermal paste: A thin grey goo between a chip and its metal cooler that fills tiny gaps so heat flows across; after years it can dry out and the chip runs hotter. More →
EDID: The menu card a TV or monitor hands over when you plug it in: its name, every picture mode it can show and whether it can do HDR, so the device can pick one. More →
eARC: A lane in an HDMI cable that carries sound back from the TV to a soundbar or receiver; the enhanced version is wide enough for full-quality surround sound. More →
HDCP: A secret password check that films and TV apps use to make sure every box between the player and the screen is allowed to show them; if one isn't, the film goes black. More →
Screen tearing: A line across the picture where the top shows one frame and the bottom the next, because the screen swapped pictures halfway through drawing. More →
V-Sync: Making a game hand new pictures to the screen only between redraws, which stops tearing but can add judder and a little delay. More →