A grace period is an additional amount of time the tenant can pay their rent past it’s due date without penalty. For example, if you set a grace period of 3 days and rent was due on the 1st, that means the tenant can pay on the 2nd, 3rd, and 4th (3 days) without penalty. Late fees would then kick in on the 5th.
Landlords often get this wrong in their lease – double check yours!