The measure of the doorframe's opening. Measured from the floor to the head rabbet vertically and between the jam rabbets horizontally. Larger than the actual size of the door itself: it also includes room for clearance.
The size of a door frame opening, measured horizontally between jamb rebates and vertically between the head rebate and the finished floor. The opening size is usually the nominal size and is equal to the actual door size plus clearances.