An Ace with any 10, Jack, Queen, or King is a Blackjack.  If you have a Blackjack, the dealer pays you one-and-a-half times your bet  unless the dealer also has a Blackjack, in which case it's a push  and neither wins.

Best Blackjack Hands\n\n The best hand is a combination of a 10, J, Q, or K alongside an Ace, better known as a blackjack. The associated potential winnings are often greater than 2-fold. For most tables, a 1.00 bet will award 2.50 for a blackjack win, with the odds being 3:2 or 2.5x the stake size.