Edges and vertices4
Schläfli symbol{4} (for square)
Areavarious methods, usually base time height
Internal angle (degrees)90° (for square and rectangle)

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 so it's like triangle, and sometimes tetragon to be like pentagon (5-sided) and hexagon (6-sided).

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

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

All the sides of a quadrilateral are straight, and the interior angles of a quadrilateral add up to 360°.

${\displaystyle \angle A+\angle B+\angle C+\angle D=360^{\circ }.}$

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.

There are 6 special kinds of quadrilaterals; square, rectangle, rhombus, parallelogram, kite, and trapezoid. Although squares, rectangles, and rhombuses are technically types of parallelograms.