A hand busts when its total is 22 or more. Because players act before the dealer, a player who busts loses the bet immediately, and the dealer does not need to play that hand out. This is a major source of the house edge in blackjack, because the player can bust before the dealer has to take any risk. Basic strategy sets out when to hit and when to stand in order to manage the chance of busting. In poker, the word is sometimes used for being knocked out of a tournament.
Example
A player holds 10 and 6 for 16 and takes a card. Drawing a 7 makes 23, so the hand busts and loses.