Something in-between.
Officially it is an image format that supports multiple images in a single file.
It doesn’t even require having multiple frames. You can have a single frame static gif which is just an image
It’s a moving picture. First used as a distribution method for silent movies on early bulletin board systems, GIF stands for Gentleman’s International Film.
Technically .gif is a file extension, GIF file is simply a bitmap image format.
Sure, they can contain one frame and look like a static image, You can insert frames from a movie into them so they can appear as a silent video. Half seriously, they are glorified image slideshows with option to contain just a single slide.
So… they land somewhere between images and animations or — if you want to be precise — images with option to be animated.
It’s a gif