In architecture a quadrangle, or more colloquially, quad, is a space on a college or university campus usually but not always enclosed on four sides by buildings. Quadrangles are descended from the cloister gardens of medieval monasteries, which were usually square or rectangular gardens or lawns enclosed by open arcades. The conversion of many monastic buildings at Oxford and Cambridge to secular colleges set the pattern for green space kept private from persons not members of the college. Some gardens are further reserved to the fellows or senior members.

In America Thomas Jefferson's design for the University of Virginia centered the housing and academic buildings around the Lawn, a huge grassy expanse. Later American college and university planners imitated either the Jeffersonian plan, the Oxbridge idea, or a combination of the two.

Despite the obvious relationship of the word "quadrangle" to the number 4, architects do not feel bound by a strict numbering of sides.

The word "quadrangle" is also sometimes, but not very often, used to mean a quadrilateral.

On television shows, the word "quadrangle" can also mean a romantic entanglement not unlike a love triangle, except with four members instead of the traditional three.