The object of the game is to draw cards that add up to 21 or as close to 21 as possible without going over (bust). Blackjack is an Ace and any Ten-value card on the first two cards dealt. Blackjack pays 3-2.
Blackjack and 21 are essentially the same game, with the objective being to reach a hand value of 21 or as close to it as possible without going over. In some cases, the term "21" may be used to refer to the game played in a casual setting, while "Blackjack" is often used in a casino context.