Graphics Interchange Format (GIF) is one of the file formats used to display indexed-color graphics and images in HTML documents on the web.
Indexed color means that it only displays a maximum of 256 colors. For this reason, GIF is NOT a good format for saving photographic type images with many colors.
GIF is good for saving images with flat blocks of color such as logos or simple illustrations.
Another very important feature of GIF images is that it allows you to preserve transparency. It uses an LZW-compressed format designed to minimize file size.