Grace period
The time between the end of a credit card billing cycle and the due date, when new purchases are interest-free if you paid in full.
If you pay your full statement balance by the due date each month, most cards charge no interest on purchases. Federal rules require the due date to be at least 21 days after the statement is mailed or delivered.
Carry a balance and you usually lose the grace period, so new purchases start building interest right away. It often takes paying in full for a month or two to get it back. Cash advances usually have no grace period.