GIF stands for Graphics Interchange Format.
GIF files or GIFs are an image file format commonly used on the internet. They are bitmap graphics and better suited to images with blocky colour and simple shapes and sharp edges, whereas a JPG bitmap graphic would be better suited photography and subtle shading.
They are also restricted to a palette of only 256 colours but do have other advantages over the JPG alternative which are lossless compression and animation.
When a GIF is compressed it does not lose any quality. This leads to less compression than a JPG can achieve.
In general GIF animations are short and simple due to the large file size but they are still very popular even with modern video alternatives. They do not store any sound data so GIF animations are always silent.