47 terms
Glossary
Plain-English definitions of the file, image, audio, video and web terms behind every tool. No jargon.
Ever wondered what WebP, OCR, bitrate or a favicon actually is? Each entry gives a clear definition, why it matters, and the free tools that work with it.
Documents & data
- Base64Base64 is a way of encoding binary data (like an image or file) into plain ASCII text using 64 safe characters. It lets you embed or transmit binary content through systems that only handle text, such as email, JSON or data URIs.
- CSVCSV (Comma-Separated Values) is a plain-text format for tabular data: each line is a row and commas separate the columns. It's the simplest, most universal way to move spreadsheet data between programs, databases and code.
- DOCX (Word)DOCX is the standard Microsoft Word document format. It stores editable text, formatting, images and layout, and opens in Word, Google Docs and Pages. It's the format for documents you're still working on. Unlike PDF, which is for finished, fixed files.
- JSONJSON (JavaScript Object Notation) is a lightweight, text-based format for structured data, built from key–value pairs and lists. It's the standard way apps and APIs exchange data because it's easy for both humans and machines to read.
- JWTA JWT (JSON Web Token) is a compact, signed token used to prove identity between systems: most commonly to keep a user logged in via an API. It packs claims (like a user ID and expiry) into a Base64 string with a signature that lets the server verify it wasn't tampered with.
- MarkdownMarkdown is a lightweight way to format plain text using simple symbols (# for headings, * for emphasis, - for lists) that convert to clean HTML. It lets you write formatted documents fast without a word processor, which is why READMEs, notes and docs use it.
- OCROCR (Optical Character Recognition) is technology that reads the text inside an image or scanned document and turns it into real, selectable, searchable text. It's what makes a photo of a page copyable instead of just a picture.
- PDFA PDF (Portable Document Format) is a file type that preserves a document's exact layout (fonts, images and formatting) so it looks identical on any device or printer. It's the standard for sharing finished documents like reports, contracts, invoices and resumes.
- RegexA regex (regular expression) is a compact pattern that describes and matches text, for example, all email addresses or every date in a document. Developers use it to search, validate and replace text with precision.
- UUIDA UUID (Universally Unique Identifier) is a 128-bit value (written as 36 characters like 550e8400-e29b-41d4-a716-446655440000) designed to be unique across space and time without a central authority. Developers use it as an ID that won't collide even when generated on different machines.
- XMLXML (eXtensible Markup Language) is a text format that stores data in nested, custom tags, like HTML but for arbitrary data rather than web pages. It's used for configuration, data exchange, sitemaps and document formats, prized for being both human-readable and strictly structured.
- YAMLYAML is a human-friendly data format that uses indentation instead of brackets, making it easy to read and write. It's the go-to for configuration files (CI pipelines, Docker Compose, Kubernetes) where clarity matters more than compactness.
Images & graphics
- Aspect ratioAspect ratio is the proportional relationship between an image or video's width and height, written like 16:9 or 1:1. It defines the shape of the frame, and matching the required ratio is what stops a platform from awkwardly cropping or stretching your content.
- AVIFAVIF is a modern image format based on the AV1 video codec. It compresses photos even smaller than WebP at the same quality and supports transparency and HDR, making it one of the best formats for fast-loading websites, though support is still slightly behind WebP.
- FaviconA favicon is the small square icon that represents a website: shown in the browser tab, bookmarks and history. It's typically a simple logo or letter exported at tiny sizes (16, 32 and 48 pixels) so it stays legible when shrunk.
- GIFA GIF (Graphics Interchange Format) is an image format best known for short, silent, looping animations. It's limited to 256 colors, which keeps simple loops small but makes it a poor choice for detailed video or photographs.
- HEICHEIC (High-Efficiency Image Container) is the format Apple devices use to save photos. It stores images at high quality in roughly half the size of a JPG, but it isn't supported everywhere, which is why non-Apple devices often can't open.heic files.
- Image compressionImage compression reduces an image's file size. Lossy compression (JPG, WebP) discards detail your eye barely notices for big savings. Lossless compression (PNG) shrinks the file while keeping every pixel. The right kind depends on whether small size or perfect fidelity matters more.
- JPG (JPEG)JPG (also written JPEG) is the most common photo format. It uses lossy compression to make photographs small by discarding detail your eye barely notices, which is why it's ideal for pictures but poor for sharp graphics, text or transparency.
- PNGPNG (Portable Network Graphics) is a lossless image format that supports transparency. Because it never degrades on save and keeps sharp edges, it's the go-to format for logos, icons, screenshots and any graphic with text or a transparent background.
- Resolution (DPI/pixels)An image's resolution is how many pixels it contains, its width × height (e.g. 1920×1080). More pixels mean more detail and a larger file. DPI/PPI describes how densely those pixels print or display. It only matters relative to physical output size.
- SVGSVG (Scalable Vector Graphics) is an image format that describes graphics as mathematical shapes and paths rather than pixels. Because it's vector-based, an SVG stays perfectly sharp at any size (from a favicon to a billboard) and is usually a small, text-based file.
- TIFFTIFF (Tagged Image File Format) is a high-quality, typically lossless image format used in photography, printing and scanning. It preserves maximum detail and supports layers and multiple pages, but the files are large, so it's an archival/print format, not a web one.
- Transparency (alpha)Transparency (the alpha channel) is the part of an image that has no color, letting whatever is behind it show through. A transparent PNG of a cut-out subject can be placed on any background, a color, a photo, or a web page.
- Vector vs rasterRaster images (JPG, PNG, GIF) are grids of pixels. They have a fixed resolution and blur when enlarged. Vector images (SVG) are defined by mathematical shapes, so they scale to any size without losing sharpness. The right choice depends on whether you need photos or scalable graphics.
- WebPWebP is a modern image format from Google that makes photos and graphics significantly smaller than JPG or PNG at similar quality. It's designed for the web to speed up page loads, and supports both lossy and lossless compression plus transparency.
Audio & video
- BitrateBitrate is how much data is used per second of audio or video, measured in kbps or Mbps. A higher bitrate means more detail and a larger file. A lower bitrate means a smaller file with more compression. It's the main dial for the quality-versus-size trade-off.
- CodecA codec is the method used to compress and decompress audio or video: it's the 'how' inside a file. H.264, H.265 (HEVC) and AV1 are common video codecs. A file's container (MP4, MOV) is separate from its codec, which is why two MP4s can behave differently.
- MOVMOV is Apple's QuickTime video format, the default for videos recorded on iPhones and Macs. It's high quality and works natively in Apple's ecosystem, but some Windows PCs, apps and platforms can't play it, which is why MOV is often converted to MP4.
- MP3MP3 is the most universal audio format. It uses lossy compression to shrink sound files to a fraction of their original size with little audible difference, which is why it plays on virtually every device, player and phone.
- MP4MP4 is the most widely supported video format, a container that holds video and audio together. Because virtually every device, editor, browser and platform plays MP4, it's the safe default for sharing, uploading and playing video anywhere.
- WAVWAV is an uncompressed, lossless audio format that stores sound at full quality. It's the standard for recording, editing and mastering because nothing is discarded, but the files are large, so you convert to MP3 for everyday listening and sharing.
- WebMWebM is an open, royalty-free video format built for the web. It typically produces smaller files than MP4 at similar quality, which makes it great for fast-loading web video, though MP4 still has broader support across devices and editors.
Web & SEO
- Canonical URLA canonical URL tells search engines which version of a page is the 'main' one when the same or similar content is reachable at several addresses. Set with a rel="canonical" tag, it consolidates ranking signals onto one URL and prevents duplicate-content dilution.
- Meta descriptionA meta description is a short HTML tag summarising a page's content. Search engines often show it as the snippet under your title in results, so a clear, unique description acts like ad copy. It doesn't directly boost rankings but strongly affects whether people click.
- Open GraphOpen Graph is a set of meta tags (og:title, og:description, og:image) that control how a link looks when shared on social media and messaging apps. They produce the title, description and preview image in the share card, without them, a shared link often appears blank.
- QR codeA QR code is a square barcode that a phone camera can scan to instantly open a link, connect to WiFi, save a contact or show text. It bridges the physical and digital worlds: print one on a poster, menu or card and people reach your content in a tap.
- robots.txtrobots.txt is a plain-text file at a site's root that tells search-engine crawlers which URLs they may or may not crawl. It's used to keep crawlers out of admin, duplicate or low-value areas and to point them at the sitemap, but it controls crawling, not privacy.
- Structured data (Schema)Structured data is machine-readable markup (usually Schema.org JSON-LD) that describes a page's content to search engines. It makes a page eligible for rich results (FAQ drop-downs, star ratings, recipe cards, article listings) that stand out in search and can lift click-through.
- UTM parametersUTM parameters are tags added to a link's end (utm_source, utm_medium, utm_campaign…) that tell your analytics where a click came from. They let you measure which campaign, channel or post drove traffic and conversions, without changing the page the link opens.
- XML sitemapAn XML sitemap is a file listing a website's URLs so search engines can discover and index them efficiently. It doesn't guarantee ranking, but it helps Google and Bing find every important page (especially on large or new sites) and speeds up indexing of fresh content.
AI & search
- AI crawlerAn AI crawler is an automated bot that fetches web pages on behalf of an AI company, either to train a model, to build a search index that AI answers cite from, or to read a page live when a user asks about it. Each purpose is a separate bot with its own name in robots.txt.
- AI searchAI search is any system that answers a question in prose instead of returning a list of links, usually citing the sources it drew on. ChatGPT Search, Perplexity, Claude's web search and Google's AI Overviews are all examples, and each retrieves live pages rather than answering purely from training.
- Generative Engine Optimization (GEO)Generative Engine Optimization (GEO) is the practice of making a website usable by AI answer engines like ChatGPT, Claude, Perplexity and Google's AI features, so they can crawl it, read it without JavaScript, and quote it as a source. It overlaps with SEO but optimizes for being cited rather than ranked.
- GPTBotGPTBot is OpenAI's web crawler that collects pages as training data for future models. It is not the bot behind ChatGPT Search results, and blocking it does not remove you from ChatGPT's answers. That is a different bot called OAI-SearchBot.
- llms.txtllms.txt is a proposed convention for a Markdown file at your domain root that gives AI systems a curated map of your site: a name, a one-line summary and grouped links. It is optional, and Google has stated its AI search does not use it.
- Retrieval-Augmented Generation (RAG)Retrieval-Augmented Generation (RAG) is how an AI answers using sources it was never trained on: it splits documents into chunks, finds the chunks that match the question, and hands only those fragments to the model. It is why your page is read as pieces rather than as a whole.
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