Poker: A Joker can be wild, or can be a "bug", a limited form of wild card which can be used only to complete straights and flushes. War: In some variations, beats all other cards. Pitch: A point card in some variations. Jokers usually are marked as "high" and "low", one outranking the other.
The jokers are two extra cards added to a deck of cards generally with pictures of court jesters. They are sometimes (although not often) used as wild cards in poker. Most card games remove the jokers from the deck before the action starts.