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.
Most sportsbooks will automatically give you your free bets once you register. However, some require you to opt in for the offer. Once you do this, you should receive your free bets.