When you play for real money, you will be required to meet the playthrough requirements before you can cash out your winnings. The playthrough is the number of times that you are required to wager the bonus amount, your deposit, or both before you can make a withdrawal.
For instance, if a bonus or deposit has a playthrough requirement of 35x, it means that you must wager it a total of 35 times before you are allowed to make a cashout.