Plain answers to file questions
Short, plain definitions of the terms behind everyday file work. Every entry ends with a private tool that runs in your browser, so you can act on what you just learned without uploading anything.
The entries are grouped by the kind of file they deal with: PDFs, images, data and security. Each one says what the term means, why it matters when you handle a real file, and what usually goes wrong, such as a photo that turns sideways after an upload or a spreadsheet that loses its leading zeros. Read the definition first, then use the linked tool on your own file.
Image
CMYK vs RGB The difference between the color model screens use and the one printers use, and why a design looks duller once it is printed. HEIC Apple's modern photo format, about half the size of a JPG at similar quality, but many websites, apps, and Windows tools cannot open it. Lossy vs lossless The difference between compression that discards detail to save space and compression that keeps every pixel, and when each is the right choice. OKLCH A colour format built on perceived lightness, chroma and hue, so equal lightness looks about equally bright, which HSL does not deliver. WebP A modern image format that makes photos and graphics smaller than JPG or PNG at similar quality, with lossy, lossless, and transparency support.
Data
Base64 A way to represent binary data, like an image, using only plain text characters. It is not encryption, since anyone can decode it. Colspan and rowspan Attributes that let one table cell cover several columns or several rows. They are how merged cells are written in HTML. HTML entity A way of writing a character that would otherwise change what the surrounding markup means, so it shows as text instead of being read as code. Number base How many distinct digits a numbering system uses before it carries into the next column, with ten in decimal, two in binary, and sixteen in hexadecimal. Percent-encoding The way a URL writes a character it cannot hold as itself, a percent sign and two hexadecimal digits, as %20 for a space. Transpose Swapping the rows and columns of a table, so the first row becomes the first column and a value in row two, column seven lands in row seven, column two. TypeScript interface A named description of an object's shape in TypeScript, listing each property and its type, so code that reads the object can be checked. Zero-width space An invisible character, U+200B, that takes up no room on screen but is still part of the text, so it can stop a search or a password from matching.
Security and privacy
EXIF data The hidden metadata your camera writes into a photo, including GPS location, device, and timestamp, and it travels with the file. JWT A compact, signed token with a header, payload, and signature that carries claims between a server and an app, used for login and authorization. Metadata The hidden data inside a file that describes it, like author, dates, location, and software used, which is easy to overlook before sharing.