- In geometry, a square is a regular quadrilateral, which means that it has four equal sides and four equal angles (90-degree angles, or 100-gradian angles or right angles).
 - It can also be defined as a rectangle in which two adjacent sides have equal length.
 - A rhombus with a right vertex angle
 - A rhombus with all angles equal
 - A parallelogram with one right vertex angle and two adjacent equal sides
 - A quadrilateral with four equal sides and four right angles
 - A quadrilateral where the diagonals are equal, and are the perpendicular bisectors of each other (i.e., a rhombus with equal diagonals)
 
Facts
Perimeter
Area
Equation (where x & y are sides)