What is MOV?

QuickTime, and what a Mac or an iPhone records into. Structurally it's almost the same file as an MP4 - both grew from the same specification - but plenty of software sees the extension and refuses anyway, which is the entire reason MOV to MP4 is a conversion people need.

What is GIF?

Thirty-five years old and still everywhere, because it does one thing nothing else quite does: animate inline, silently, in any context that displays an image. The cost is a 256-colour palette and no real motion compression, which makes GIF a poor way to store video and an excellent way to send a three-second loop.