1. A room (or several rooms, or the entire basement floor) that is partially or entirely below grade; relatively cool in the summer and above freezing in the winter; often used as storage space; provides some thermal insulation airspace
between the ground or concrete slab and the flooring of the wood floor above.
2. That
part of a building having at least half of its clear height below grade. Also see earth cellar, root cellar, storm cellar, basement.