Which of the following best describes a trapezoid?

A trapezoid is best described as a quadrilateral that has exactly one pair of parallel sides. This definition captures the essential characteristic that distinguishes trapezoids from other types of quadrilaterals, such as rectangles, which have two pairs of parallel sides.

A trapezoid can be further classified into different types, such as isosceles trapezoids, which not only have one pair of parallel sides but also have the non-parallel sides equal in length and the angles at each base equal. In contrast, the other descriptions do not accurately represent the key feature of trapezoids. For instance, a quadrilateral with equal angles describes a rectangle, while the statement about a polygon with five sides refers to a pentagon, which is unrelated to trapezoids. Consequently, the definition of having exactly one pair of parallel sides is the defining trait of a trapezoid.