What is artificial intelligence? And what is the difference between human intelligence and artificial intelligence?

With respect to computer games:

AI (artificial intelligence) is program code that controls the behavior of characters/unit/targets/etc not directly controlled by a player in a game.

it is limited to just what it needs to do for purposes of the game. this typically includes some basic target selection, movement, and attack behavior. or in more general terms, goal selection, movement, and action execution behaviors.

everything that humans can do beyond this is the difference between the two.