Yes, I agree credit cards use the term "grace period" under the terms of the card (in the "fine print") as applied to the window in which interest does not accrue.
However, if you call them they will also use the colloquial term "grace period" as a term that applies to how many days late your payment can be (I don't know how it would be termed in your agreement - and would probably differ from bank to bank). They have different due dates - one date they tell you the payment is due, the actual date the payment is due (known by them - but often 5-7 days later), and a date they will begin reporting a late payment to the bureaus. If you call and ask them the different dates they will probably be happy to tell you. If you have a high risk card then the payment due date on your statement may be the same date it is actually due.