A wagering or turnover requirement is the total value of bets you must place before bonus credit, and sometimes your own deposit, can be withdrawn. It is usually written as a multiple, such as 10x, of the bonus or of the bonus plus deposit.
Illustrative example only, using round numbers rather than real P999 figures: if an account receives a bonus of 100 with a 10x turnover rule on the bonus, the player must place 1,000 in total bets before the bonus balance becomes withdrawable. If the rule applies to bonus plus a deposit of 100, the target doubles to 2,000.
Turnover counts the amount staked, not the amount won. Ten bets of 100 meet a 1,000 target whether they win or lose. Over that many bets the house edge works against the balance, which is why many players finish the requirement with less than they started with, or nothing at all.
Some games may count at a reduced rate or not at all towards turnover, and there may be a maximum bet while a bonus is active. Breaking those rules can lead to the bonus and any winnings being removed.