Trapezoids are one of the most common quadrilaterals. A trapezoid is a quadrilateral having two, and only two, parallel sides. The bases of the trapezoid are its parallel sides; the legs are its non parallel sides. When a trapezoid has two sets of parallel sides, it is a more specific type of trapezoid called a parallelogram. A more specific type of trapezoid is called an isosceles trapezoid. An isosceles trapezoid is a trapezoid with congruent sides. Trapezoid principles.
