In blackjack, insurance is a side bet that protects against the dealer having a natural when the up card is an ace. The stake is half of the main bet, and it pays 2 to 1. So if the dealer does have blackjack, the insurance win covers the lost main bet and the player breaks even on the round. That is where the name comes from.
Whether to take it is another matter. Insurance wins only when the hole card is a ten-value card, which happens less than one time in three, yet the 2 to 1 payout needs exactly one in three to break even. In multi-deck games that gives the bet a house edge of roughly 7%, so basic strategy says decline it unless you are counting cards. If the dealer has no blackjack, the insurance is lost and the main bet can still lose too. For operators, insurance is a standard rule setting in RNG and live blackjack.