Google talks about 'returning visitors'. Casinos do not look for returning visitor, they need returning players. More specific: not that kind of players looking after free spins or demo games. Their aim is that players effective spend cash. One of the used tricks to get them revisiting their casino is the cashback bonus. In other words: casinos offer a cash back of your deposited cash.
A casino cashback offer will differ from casino to casino. In general this bonus 'compensates' a percentage of the player’s losses within a specific time frame. There are 2 options: or you receive cash cash back, or the bonus is given in the form of credits in your account. In this second scenario, you can play with your credits in future gambling sessions.
The most common cashback offer may be 20% each week. This means that a player loosing $100 during his playing time at the online casino during 1 week, will be credited back $20 during the next week. There are several options possible: the cashback is delivered within 48 hours, daily, within a week, or next day.
The same case with regard to the percentage you get returned. This can vary from 100%, over 50%, 30%. 20% etc to 1%. Of course, players appreciate and enjoy the advantage of seeing some of their cash returned to them. But... they have to continue playing at the casino to enjoy the cash if they play again!