What is the defining characteristic of a trapezoid?

The defining characteristic of a trapezoid is that it has only one pair of parallel sides. This is a fundamental property that distinguishes trapezoids from other quadrilaterals. In a trapezoid, the sides that are parallel are referred to as the bases, while the other two sides, which are not parallel, can vary in length.

This single pair of parallel sides is what allows trapezoids to have unique properties, such as the possibility of non-equivalence in the lengths of the other sides, and asymmetrical shapes depending on their configurations. Other types of quadrilaterals, such as parallelograms or rectangles, have two pairs of parallel sides, which fundamentally changes their structure and properties.

Understanding this characteristic is key to recognizing and differentiating trapezoids in geometry.