Casinos attach wagering requirements to their bonuses. 50x wagering means you need to play through your bonus 50x before you can withdraw your winnings. In a case of a 100% up to $100 deposit bonus with a 50x wagering requirement, you deposit $50 and get a $50 bonus. With a 50x wagering requirement, you need to turn around the $50 bonus x 50 = Play with $2500.