A plane figure having four equal sides and four interior right angles. Photo from Virginia State Capitol, Richmond, Virginia, 2021. 2. An area of flooring, roofing, or the like, 10 feet square. 3. An open or parked rectangular space in a community. 4. An instrument, sometimes combined with measure, for determining right-angledness. 5. Adjective, descriptive of lines or planes at right angles to each other. 6. A unit for measuring roofing materials, equal to 100 square feet (9.3 square meters) of coverage.