Is there a term for preloading video?

Solution 1:

The word you are looking for is buffer. Since the playback speed of a video is typically faster than the download speed, the video can't be played immediately. As it is downloaded, it is buffered until there is enough data stored to be able to play the video at its proper speed while the rest of the data is downloaded.

Solution 2:

Depends on whom you're addressing. You're probably asking the wrong people. Videophiles may well have a specific term for this.

You could make one up or adapt a general term like caching or buffering as suggested in the comments if you want to. But in a language where we still talk about dialing a telephone anything can happen.