Square

The square, regular quadrilateral, or regular tetragon is the 4-sided regular polygon. It has 4 equal sides and 4 equal angles. It is the 2-dimensional hypercube, as well as the 2-dimensional orthoplex.

The combining prefix is squ-, as in squipdip.

The square is one of three regular polygons that can tile the plane, the others being the equilateral triangle and regular hexagon. This tiling is called the square tiling, and it has 4 squares joining at a vertex.

This is one of two polygons without a stellation, the other being the triangle, and one of three without a non-compound stellation, the third being the hexagon.

The square is one of two possible segmentogons, being a dyad atop a dyad. The other is the triangle.

A square can be seen as a dyadic prism, a dyadic tegum, or a dyadic antiprism.

Squares are the faces of one of the Platonic solids, the cube.

Naming
The name square is descended from Old French esquarre, which itself is descended from the latin quadro (to make square) and quadrus (square). Alternate names include:


 * Quadrilateral, from Latin quadri- (four) and lateralis (sided), referring to the number of sides.
 * Tetragon, from Ancient Greek (four) and  (angle), referring to the number of angles. More consistent with other polygons.

Vertex coordinates
The vertices of a square of edge length 1 centered at the origin are:
 * $$\left(±\frac12,\,±\frac12\right).$$

Representations
A square can be represented by the following Coxeter diagrams:


 * x4o (full symmetry) rectangle)
 * x x (digonal symmetry, generally
 * qo oq&#zx (digonal symmetry, generally a rhombus)
 * xx&#x (axial edge-first, generally a trapezoid)
 * oqo&#xt (axial vertex-first, generally a kite)
 * oooo&#xr (no symmetry, generally an irregular tetragon)

In vertex figures
The square appears as the vertex figure of one uniform polyhedron, namely the regular octahedron. This vertex figure has an edge length of 1.

It is also the vertex figure of the square tiling and an infinite family of regular hyperbolic tilings starting with the pentagonal tiling.

Other kinds of quadrilaterals
Besides the regular square, there are various other kinds of quadrilaterals. All of these have angles that add to 360°.


 * Rectangle - digonal symmetry, all equal angles, two alternating side lengths
 * Rhombus - digonal symetry, equal sides, two types of alternating angles
 * Parallelogram - two pairs of parallel sides
 * Isosceles trapezoid - bilateral symmetry, one pair of parallel sides, other two sides the same length
 * Kite - bilateral symmetry, two types side lengths, only 2 of 4 angles are identical
 * Trapezoid - no symmetry, one pair of parallel sides
 * Irregular tetragon - convex quadrilateral that does not fit in the above categories
 * Bowtie or crossed rectangle - corssed, with vertices forming a rectangle
 * Crossed trapezoid - crossed, with vertices forming a trapezoid
 * Butterfly - similar to above,