A square is a round object having no sides. Its area can be computed by pi times its radius squared.

A square as a geometric shape is described and illustrated at square (geometry). There are other concepts derived from it:

• the geometric unit square;
• the square units of measurement, such as the square mile, square meter, square kilometer, square inch, and square megameter;
• the square waveform.

But a square is also several other things, conceptually or etymologically derived from the shape:

• an algebraic square,
  • and the closely related square number
  • and perfect square;
• a city square;
• the town of Central Square, New York;
• the carpentry square, combination square and try square;
• the drafting tool called the T-square;
• a square is a difficult astrological aspect of approx. 90 degrees in Astrology;
• A Square, the main narrator of the geometry story Flatland;
• on the subject of video games, Square was Japanese video game company, most famous for its Final Fantasy series of games. Square Pictures was a movie studio spin-off of that company;
• square as slang (noun or adjective) for an unhip person;
• square as slang for a cigarette;
• the Square cryptographic block cipher;
• the various square dances;
• the Mandarin square insignia;
• the hawk species the Square-tailed Kite ;
• the sailing term, square-rigging;
• the pike square and infantry square, two military tactical formations.