 A closed plane figure bounded by 4 sides or line segments is called a quadrilateral.
In the given figure, ABCD is a quadrilateral whose four sides are AB, BC, CD and AD. There are four interior angles in a quadrilateral and the sum of the angles of a quadrilateral is always 360°.

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There are some special types of quadrilaterals. They are:

#### Rectangle:

A quadrilateral having its opposite sides equal and each angle 90° is called a rectangle. ABCD in the given figure is a rectangle.
In a rectangle,
1.       Diagonals are equal and they bisect to each other.
2.       Opposite sides are equal and parallel.
Area of rectangle = l × b, where l is length and b is breadth of rectangle

#### Square:

A quadrilateral having its all four sides equal and each angle 90° is called a square. ABCD in the given figure is a square.
In a square,
1.       Diagonals are equal and they bisect to each other at 90°.
2.       Opposite sides are equal and parallel.
Area of square = l2, where l is length of square

#### Parallelogram:

A quadrilateral having opposite sides parallel is called a parallelogram. ABCD in the given figure is a parallelogram.
In a parallelogram,
1.       Opposite sides are equal.
2.       Opposite angles are equal.
3.       Diagonals bisect each other.
Area of parallelogram = b × h, where b is base and h is height of parallelogram

#### Rhombus:

A quadrilateral having its all four sides equal is called a rhombus. ABCD in the given figure is a rhombus.
In rhombus,
1.       Diagonals bisect to each other at 90°.
2.       Opposite sides are parallel.
3.       Opposite angles are equal.
Area of rhombus = ½ × d1 × d2, where d1 and d2 are diagonals of rhombus

#### Kite:

A quadrilateral having its adjacent sides equal is called a kite. ABCD in the given figure is a kite.
In kite,
1.       Diagonals intersect each other at 90°.
Area of kite = ½ × d1 × d2, where d1 and d2 are diagonals of kite

#### Trapezium:

A quadrilateral having a pair of its opposite sides parallel is called a trapezium. ABCD in the given figure is a trapezium.
Area of trapezium = ½ × h × (l1 + l2), where h is height and l1 and l2 length of parallel sides