Blackjack is a casino banking game. It is the most widely played casino banking game in the world. It uses decks of 52 cards and descends from a global family of casino banking games known as "twenty-one". This family of card games also includes the European games vingt-et-un and pontoon, and the Russian game Ochko. Blackjack players do not compete against each other. The game is a comparing card game where each player competes against the dealer.

Games available in most casinos are commonly called casino games. In a casino game, the players gamble cash or casino chips on various possible random outcomes or combinations of outcomes. Casino games are also available in online casinos, where permitted by law. Casino games can also be played outside of casinos for entertainment purposes, like in parties or in school competitions, on machines that simulate gambling.