Wagering requirements are conditions that must be met before you can withdraw any winnings from a new no deposit bonus. They are usually given as a multiple of the bonus amount.
For example, if the bonus has a 10x wagering requirement and you receive a $10 bonus, you will need to wager $100 before you can withdraw any winnings.
The wagering requirements for no deposit bonuses can vary greatly. Some can be very hard to satisfy.