A Gif (Graphics Interchange Format) file format has a limited palette and lossless compression. This means that, in comparison to a Jpeg file, the colours in a gif image will be flattened but the overall image will not be degraded when it is saved. A gif can also support transparency.
A gif can be used for a number of projects especially online including logos and games but it is probably best know for small animations and lo-res video clips.
If you’ve ever wanted to try out your animation skills, creating a short gif is a great starting point.
Here is a video from Adobe about using Photoshop to create a gif.
Or a for a slower instructional video for CS6 can try IRecordIn3D’s tutorial who animates a photo.
Here’s my first attempt at a gif animation.