The "surrender" rule in Blackjack allows players to give up their hand and lose only half of their bet, typically before taking any action. It can be used when the player feels their chances of winning are low, especially when facing a strong dealer upcard like a 9, 10, or Ace. There are two types: early surrender, which is more favorable as it allows the player to surrender before the dealer checks for Blackjack, and late surrender, which is only available after the dealer’s Blackjack check. Using surrender is a strategy to minimize losses in situations where the player is unlikely to win.