This is often found in the terms and conditions of casino and some sports offers.
A x6 wagering requirement on a Sports bet means that you need to bet that bonus 6 times before you can withdraw it.
So if you receive a £50 bonus which requires a 6xWR then you need to either lose the bonus (bust out) or bet £300 before it becomes withdrawable. The best result is usually to lose the first bet so that you’re clear as soon as possible, although account protection should be given some consideration.
The bonus funds usually have an expiry date at which point they are removed, this is usually a fairly long period but can on occasion be short so it’s worth checking, especially if you end up with a large amount of bonus funds after winning your first bet.