A wagering requirement is a multiplier that represents the number of times you have to play though a bonus before you are able to withdraw any winnings. For example: I am given a 20 Casino bonus with a 10x wagering requirement.
Wagering multiples: When a casino specifies a 40x wagering requirement, it means that you need to bet 40 times the bonus amount or the sum of your deposit and bonus before you can make a withdrawal.