Definition
GIF (Graphics Interchange Format) is a bitmap image format released by CompuServe in 1987. It uses lossless LZW compression, allows at most 256 colors per frame, and supports frame-by-frame animation; the version in common use is defined by the 1989 GIF89a specification.
How it works
A GIF stores images as palette-indexed frames of pixels; playing several frames in a loop with set delays produces an animation. Compression loses no pixel data, but the 256-color ceiling limits GIF for gradients and photographic content.
Usage
Animated GIFs are ubiquitous in memes, social networks and short looping animations on the web. Requiring no player and working everywhere, GIF is among the most widely shared image formats in internet culture.
Related and confusable terms
GIF is a bitmap format whereas SVG is a vector format; whether an image stays sharp when enlarged is the key difference. Like SVG, GIF belongs to 2D imagery.