“Wagering requirements” is a term that refers to the amount of times a bonus needs to be played through before any associated winnings can be withdrawn.
Wagering requirements are never a set monetary figure. Instead, they will be a multiplier of the bonus amount received. This multiplier is set by the casino. In this case, Bonus Boss's wagering requirement is 40x, which is only applied to free bonuses and winnings from free spins.