Imgur converts most moving images into mp4 and webm, serving the optimal file to the browser the visitor is using. I think this is part of the reason why people use the word "GIF" for any moving media these days as imgur is a very popular medium.
GIF also has the connotation of the animation or video being short (under 30 seconds), often subtler animation, and without audio - whereas "video" implies more a traditional multimedia presentation.
