Trapezoid
US usage, definition 1: A quadrilateral which has a pair of opposite
sides which are parallel. The parallel sides are called the bases,
and the other two sides are called the legs.
US usage, definition 2: A quadrilateral which has one parallel pair of opposite sides and one nonparallel pair of opposite sides. The parallel sides are called the bases, and the other two sides are called the legs.
UK usage: The same as the US word trapezium. The UK word trapezium means the same as the US word trapezoid, and viceversa.
Commentary: Under US definition 1, a parallelogram is a type of trapezoid. Under US definition 2, a parallelogram is not a type of trapezoid. Regardless of which definition you prefer, the trapezoid area formula can be used to find the area of a parallelogram.
See
also
Isosceles
trapezoid, rhombus,
rectangle, square, height
of a trapezoid, trapezoid rule, polygon
