Which characteristic is true of a trapezoid?

A trapezoid is defined as a four-sided figure, or quadrilateral, that has exactly one pair of parallel sides. This characteristic distinguishes trapezoids from other quadrilaterals, such as parallelograms, which have two pairs of parallel sides. While some trapezoids may have other special properties, such as isosceles trapezoids having non-parallel sides of equal length, the primary defining trait of all trapezoids is the existence of one pair of parallel sides.

The other characteristics mentioned in the other options either apply to different types of quadrilaterals or are incorrect for trapezoids. Hence, the understanding that a trapezoid must have only one pair of parallel sides is crucial to recognizing and defining this shape in geometry.