Which shape has exactly one pair of parallel sides?

A trapezoid is defined as a quadrilateral that has exactly one pair of parallel sides. This characteristic distinguishes it from other quadrilaterals like rectangles and squares, which have two pairs of parallel sides.

In a trapezoid, the parallel sides are referred to as the bases, while the non-parallel sides are the legs. This unique feature allows for a variety of trapezoid types, including isosceles trapezoids, where the legs are equal in length but still maintains only one pair of parallel sides.

Conversely, rectangles and squares, both of which belong to a broader category of quadrilaterals known as parallelograms, possess two pairs of parallel sides. A rhombus also has this same property, presenting another pair of parallel sides. Thus, the trapezoid stands out as the only shape within this set that meets the condition of having exactly one pair of parallel sides.