A basement is one or more floors of a building that are either completely or partially below the ground floor. Basements are typically used as a utility space for a building where such items as the furnace, water heater, breaker panel or fuse box, car park, and air-conditioning system are located; so also are amenities such as the electrical distribution system, and cable television distribution point. However in cities with high property prices such as London, basements are often fitted out to a high standard and used as living space.
In British English, the word "basement" is used for underground floors of, for example, department stores, but the word is only used with houses when the space below their ground floor is habitable, with windows and (usually) its own access. The word cellar is used to apply to any large underground room. A subcellar is a cellar that lies further underneath.