Almost every sportsbook has some kind of deal to attract new bettors and there are many different methods to draw people in. First, you have to deposit at least $5 into your account and then you'll get the $20 in bonus play money, which is not redeemable for cash.
For instance, DraftKings used to have a $20 bonus play that has a number of stipulations. Most bonus bets are only available on a first deposit at that specific sportsbook.
Bonus bets in sports betting are often connected to deposits and are also referred to as bonuses.