A quadrilateral (also called a tegragon or quadrangle) is a figure made up of four coplanar segments that have four non-colinear points as their endpoints and that intersect only at those four points.

Not a quadrilateral because three of the points (A, C and D) are colinear.

Not a quadrilateral because two of the segments, and , intersect at a point other than their endpoints.

This is a quadrilateral.

Two sides of a quadrilateral that have a common end point are called consecutive sides. Two sides of a quadrilateral that don't have a common end point are called opposite sides. The segment that connects a pair of opposite vertices is called a diagonal.

In the right hand figure above we have the following examples:

Segment Type

Examples

opposite sides

and ,
and

consecutive sides

and ,
and ,
and ,
and

diagonals

and (not drawn in the figure)

Special Quadrilaterals

Name

Description

Example

trapezoid

a quadrilateral where exactly one pair of sides are parallel

isosceles trapezoid

a trapezoid where the non-parallel sides are congruent

parallelogram

a quadrilateral where both pairs of opposite sides are parallel

rectangle

a qudrilateral where all of the angles are right angles

square

a quadrilateral where all of the angles are right angles and all of the sides are congruent

rhombus

a quadrilateral where all of the sides are congruent

kite

a quadrilateral where one pair of consecutive sides are congruent and the remaining two sides are congruent but the sides in the two pairs are not congruent