In blackjack, insurance is a side bet offered to players when the dealer's face-up card is an Ace. It allows players to wager up to half of their original bet, essentially betting that the dealer has a blackjack, which is a total of 21 with an Ace and a 10-value card. If the dealer does have a blackjack, the insurance bet pays 2:1, allowing the player to recover their original bet, but if the dealer does not have a blackjack, the player loses the insurance bet. While insurance can provide a form of protection against a dealer's blackjack, it is generally considered a risky option, as the odds are not in the player's favor in the long run.