The grace period is the time during which you are allowed to pay your credit card bill without having to pay interest. The Credit CARD Act of 2009 requires that if issuers have grace periods, they must last at least 21 days. The grace period usually applies only to new purchases.
Most credit cards do not give a grace period for cash advances and balance transfers; instead, interest charges start right away. See also “How to use the grace period to avoid paying interest.”