You can draw many different shapes that have four straight sides.
On this page, we will take a look at what we know about foursided figures,
and the information associated with them.

A quadrilateral is a foursided polygon. 

A quadrilateral is basically any figure that has exactly four sides.
A quadrilateral can be any foursided figure. When we start putting conditions on how the quadrilateral should look, we find that these "special" quadrilaterals fall into categories based upon their characteristics, or properties.
We will be examining two major categories of quadrilaterals: trapezoids and parallelograms.

A trapezoid is a quadrilateral with at least one pair of parallel sides. 

NOTE: The category "trapezoids" contains quadrilaterals with only one set of parallel sides
along with quadrilaterals with two sets of parallel sides. The word "
trapezoid" is generally used to reference quadrilaterals with only one pair of parallel sides, since trapezoids with two pairs of parallel sides have their own distinctive names.
Here the word "trapezoid" is being used to reference quadrilaterals with one pair of parallel sides.
There are two basic types of these trapezoids: regular trapezoids and isosceles trapezoids.

Definition: A trapezoid has at least 1 pair of parallel sides.
Also:
• The trapezoid shown here is a quadrilateral with one set of parallel sides.


Definition: An isosceles trapezoid is a trapezoid with congruent base angles.
Also:
• The trapezoid shown here has one set of parallel sides.
• An isosceles trapezoid has legs of equal length.

Note: The definition of an isosceles triangle states that the triangle has two congruent "sides". But the definition of isosceles trapezoid stated above,
mentions congruent base "angles", not sides (or legs). To find out "Why?", go to the high school Geometry course page.
When our quadrilateral has two sets of parallel sides (instead of just one set), the quadrilateral is still a trapezoid, but it is a special type of trapezoid which has been given its own special name.

A parallelogram is a quadrilateral with both pairs of opposite sides parallel. 

The category of parallelograms will include the "basic" parallelogram along with three additional quadrilaterals that possess ALL of the properties of a parallelogram, plus several additional characteristics of their own.
NOTE: At this level, we are concentrating on the shapes of the quadrilaterals and their basic characteristics.
For more quadrilateral information go to the Geometry course section.

Definition: A parallelogram has two pairs of parallel sides.
Also:
• The opposite sides of a parallelogram are equal in length.


Definition: A rectangle is a parallelogram with 4 right angles.
Also:
• A rectangle has two pairs of parallel sides.
• A rectangle has opposite sides equal in length.


Definition: A rhombus is a parallelogram with all 4 sides of equal length.
Also:
• A rhombus has two pairs of parallel sides.
(It looks like a slanted square.)


Definition: A square is a parallelogram with 4 sides of equal length and 4 right angles.
Also:
• A square has two pairs of parallel sides.
