In the context of online slots, 'turnover' refers to the total amount of money a player must wager before they can withdraw winnings earned from bonus funds. It's also known as a wagering requirement. For example, if a player receives a bonus with a 10x turnover requirement, they must wager ten times the bonus amount before any winnings can be cashed out. Understanding the turnover requirement is crucial for managing expectations and optimizing gameplay when using bonuses.