A cashback bonus is a promotion typically offered by online casinos, sportsbooks, or poker rooms in which players are given a portion of their losses back as a reward for playing or betting. It usually involves giving a player a percentage of their losses back in the form of bonus cash, so it's essentially a form of insurance policy.
The idea behind cashback bonuses is that it will entice players to come back to the casino and play more, thus helping to create or maintain player loyalty. It’s also regarded as a way to encourage players to continue to bet even if they’re not having a great deal of luck.