Blackjack insurance is a side bet offered to the Blackjack player when the dealer gets an ace. Blackjack insurance purpose is to protect your hand against the dealer's possible Blackjack.
The player who purchases insurance should make an extra bet in the amount of up to 1/2 of his the main bet. Afterwards, in case if the dealer has a Blackjack (with the face card or 10 underneath), the players that bought insurance are paid twice the amount of their insurance bet (2 to 1). If the dealer does not have Blackjack, the insurance bet is collected and the regular Blackjack hand is played.
Even Money is another type of Blackjack insurance whenever the player has blackjack, it means that the player is paid 1 times their bet right away instead of 1.5 times (for a regular Blackjack) after showdown.
Blackjack insurance won't give you an advantage over the casino, no matter whether you win or lose on this particular bet, the casino would earn its share in cany case. Do not use Blackjack insurance if you want to be a profitable Blackjack player.