Trapezoid

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 non-parallel 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 vice-versa.

Trapezoid with parallel sides b₁ (top) and b₂ (bottom), height h, and area formula: Area = h((b₁ + b₂) / 2)

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.