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

A quadrilateral is a four-sided polygon.

A quadrilateral is basically any figure that has exactly four sides.

A quadrilateral can be any four-sided 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: This definition is the "inclusive" definition of a trapezoid, meaning that it states "at least one" instead of "exactly one" pair of parallel sides. Under this definition, the word "trapezoid" can apply to quadrilaterals with "one pair" of parallel sides, and also to quadrilaterals with "two pairs" of parallel sides.

Most often, you will see the word "trapezoid" associated with quadrilaterals with only one pair of parallel sides, since trapezoids with two pairs of parallel sides have their own distinctive names.

First, we will examine trapezoids with one pair of parallel sides. The trapezoids with two pairs of parallel sides will appear under the heading "parallelograms".

	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.