When the dealer’s up card is an ace, a player can place an insurance bet of up to half the original bet. It wins and pays 2 to 1 if the dealer has blackjack and loses otherwise. The name is misleading. It is a separate bet on whether the dealer’s hidden card is a ten value card, and for most players its long run result is negative. Basic strategy advises against taking it, apart from rare situations that depend on counting cards.
Example
A player bets 10 and takes insurance for 5. If the dealer has blackjack, insurance pays 10 and the original bet loses 10, so the player breaks even. If not, the 5 is lost.