In blackjack, split hands occur when a player is dealt two cards of the same value, allowing them to divide their hand into two separate hands. Each hand is then played independently, and players must place an additional bet equal to their original bet for the second hand. The total score for each split hand is calculated independently based on the individual cards in that hand, with the goal of reaching a total closest to 21 without exceeding it. If either hand reaches a total of 21, it's considered a blackjack if the second card is a ten-value card, which typically pays better than a regular win.