What exactly are included in Game, Draw and GPU time (that you get from "stat unit") ?

And how these are related ? Is the Game thread the main thread or there’s separate main thread running game, draw(and gpu ?) threads ?
And is it possible that draw thread is waiting on something in the game thread yet game time is much smaller than draw time for example?

This is really performance and profiling question but I would like to understand how main UE4 programs are structured and threaded etc.