What is a animated gif. ?
a graphic image on a Web page that moves - for example, a twirling icon or a banner with a hand that waves or letters that magically get larger.

what are animated gif used for ?
A GIF file can hold multiple images, which lets users create simple animations. GIFs were also one of the first two image formats used online. The format supports up to 8 bits per pixel and a palette of up to 256 distinct colors. Use GIFs for simpler images like logos with solid color areas.