From Citizendium, the Citizens' Compendium
- In elementary geometry : A regular polygon of four sides.
- In mathematics generally : Add brief definition or description
- Squaring the circle : Add brief definition or description
- Square circle : A plane shape, or object viewed from one side, that is both a square and a circle; in philosophy, a common example of an impossible object.
- In cryptology : A block cipher invented by Joan Daemen and Vincent Rijmen, and a forerunner to the Rijndael algorithm, which has been adopted as the Advanced Encryption Standard.
- Square of opposition : A diagram representing the different ways in which each of the four propositions of the system are logically related ('opposed') to each of the others.