The quadrangular space, also known as the quadrilateral space (of Velpeau) and the foramen humerotricipitale, is one of the three spaces in the axillary space.

The quadrangular membrane is a layer of submucosa.

Four-sided base, three-dimensional object.

A quadrangular castle or courtyard castle is a type of castle characterised by ranges of buildings which are integral with the curtain walls, enclosing a central ward or quadrangle, and typically with angle towers.