A building story which is wholly or less than half below ground; it is generally used for living space.

1. A complex, usually of igneous and metamorphic rocks, that is overlain unconformably by sedimentary strata. Also known as basement rock.

2. A crustal layer beneath a sedimentary one and above the Mohorovicic discontinuity.

3. The ancient continental igneous rock base that lies beneath Precambrian rocks. Also known as basal complex; basement complex.