A plane figure bounded by four sides is called a quadrilateral.  In the following figure, four line segments AB, BC, CD and DA bound a Quadrilateral ABCD.

In the given figure, we have.
a)  The points A, B, C and D are the vertices of quadrilateral ABCD.
b) The line segments AB, BC, CD and DA are the sides of quadrilateral ABCD.
c) The line segments AC and BD are called the diagonals of quadrilateral ABCD.

Points To Remember :-
a) Two sides having a common end point are called adjacent sides.
b) Two sides having no common end point are called opposite sides.
c) Two angles of a quadrilateral having a common arm are called consecutive angles.
Two angles of a quadrilateral having no common arm are called its opposite angles.

## Angle Sum Property of a Quadrilateral

The sum of all the four angles of a Quadrilateral is 3600.

Let us prove it:
In a Quadrilateral ABCD, join BD.`  Since, the sum of the angles of a triangle is 1800.
 In Triangle ABD, we have

## Types of Quadrilateral

Various types of Quadrilateral are:
a) Parallogram
b) Rectangle
c) Square
d) Rhombus
e) Trapezium
f) Kite