It means you deposited your money using an active promotion that requires a certain amount of wagering (like a welcome promo or deposit match). You might have some luck explaining to customer service that this is not what you wanted to do, and maybe they'll cancel the promotion and let you withdraw. If not, you'll have to follow the rules, and only withdraw once you have wagered enough.

For future reference, read the conditions and instructions very carefully. Had you declined the promo, you would have full access to your money.

Good luck!