A penetration, in firestopping, is an opening, such as one created by the use of a cast-in-place sleeve, in a wall or floor assembly required to have a fire-resistance rating, for the purpose of accommodating the passage of a mechanical, electrical, or structural penetrant.
The penetration may or may not contain a firestop system. A penetration (opening) may or may not include a penetrant (something passing through the opening).
See also
Sleeve (construction) Passive fire protection Annulus (firestop) Joint (building) Penetrant (mechanical, electrical, or structural) Mortar (firestop) Firestop pillow Fire test