Free Bet. With a free bet, you're making a wager without any real cash attached. If you use a free bet and win, the winnings you receive back will not include the free bet amount. Instead, you'll only receive back the amount of the winnings.
When a free bet wins, your sportsbook will only give you the profit from the wager and not the stake. This is known in the industry as a Stake Not Returned (SNR) free bet.
