|Base||One of the parallel sides. Every trapezoid has two bases. See Base definitions.|
|Leg||The sides AC and BD above are called the legs of the trapezoid, and are usually not parallel, although they could be (see parallelogram note below). Every trapezoid has two legs.|
|Altitude||The altitude of a trapezoid is the perpendicular distance from one base to the other. (One base may need to be extended).|
|Median||The median of a trapezoid is a line joining the midpoints of the two legs. See Trapezoid median|
|Area||The usual way to calculate the area is the average base length times altitude. See Area of a Trapezoid|
|Perimeter||The distance a round the trapezoid. The sum of its side lengths. See Perimeter of a Trapezoid|
If both legs are the same length, this is called an isosceles trapezoid, and both base angles are the same.
If the legs are parallel, it now has two pairs of parallel sides, and is a parallelogram.
|Trapezoid||A quadrilateral with no sides parallel||A quadrilateral with one pair of parallel sides|
|Trapezium||A quadrilateral with one pair of parallel sides||A quadrilateral with no sides parallel|