Gif Movies, or “Mini Movies”, are movies that are condensed into Gif form . These movies are usually no longer then a few minutes, since the are played in a way were you only see alternating amount of frames. E.g. Every 5th frame or every 10th frame, and so on.
The first Gif movie was actually the whole movie in its entirety, but is extremely small (probably due to size constraints). The movie was Terminator 2 and it was posted on Riddit by the user sardonically
Riddit also has a spot just for gif movies where you and go and watch over 150 movies from around the web, all in one spot. You can also place requests for movies.