What is "prediction"?

[pickleplayer]

I'm not looking for any help with specific problems at the moment. I just keep seeing this term "prediction" used in the game's code and I'm curious to know what it means or what it does, if anyone has an explanation. 

I remember a while back on this forum, I was having trouble with a different mod where I had a custom state with a custom animation that wouldn't play correctly for all players, and I couldn't figure out why. But then someone just told me to try putting "nopredict" in the state tag and it just magically fixed it.

 

 

So what does it do? I've played around with it a bit recently but couldn't really figure out what it was for. Does anyone know how it works?