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Six Quadrilaterals.svg
Some types of quadrilaterals
Edges and vertices 4
Schläfli symbol {4} (for square)
Area various methods;
see below
Internal angle (degrees) 90° (for square and rectangle)
A quadrilateral

In Euclidean plane geometry, a quadrilateral is a polygon with four edges (or sides) and four vertices or corners. Sometimes, the term quadrangle is used, by analogy with triangle, and sometimes tetragon for consistency with pentagon (5-sided), hexagon (6-sided) and so on.

The origin of the word "quadrilateral" is the two Latin words quadri, a variant of four, and latus, meaning "side".

Quadrilaterals are simple (not self-intersecting) or complex (self-intersecting), also called crossed. Simple quadrilaterals are either convex or concave.

The interior angles of a simple (and planar) quadrilateral ABCD add up to 360 degrees of arc, that is

This is a special case of the n-gon interior angle sum formula (n − 2) × 180°.

All non-self-crossing quadrilaterals tile the plane by repeated rotation around the midpoints of their edges.

All of the sides of a quadrilateral are straight and the sum of all the angles add up to 360 degrees. There are 6 special kinds of quadrilaterals; kite, rhombus, square, rectangle, parallelogram, and trapezoid. Sometimes they are called "quadrangles" or "tetragons." This type of quadrilateral are one angle greater than 180 degree.