A wagering requirement/playthrough is the amount you must wager while in a bonus before that bonus is considered to be completed.
For example, if you receive a $100 bonus with a 10× wagering requirement, you must place $1,000 in bets before the bonus is complete.
Once completed, any remaining bonus funds will be converted into unrestricted cash.
You can track your progress towards completing your wagering requirement on the "My Bonus" section of the website/app.