What defines a trapezium in terms of its sides?

A trapezium, also known in some regions as a trapezoid, is defined by having at least one pair of opposite sides that are parallel. The correct definition describes it as having two opposite sides parallel, while the other two sides are not parallel.

This means that while one set of sides reflects a parallel relationship, the other two sides do not conform to any specific requirement of being parallel or equal in length. Other definitions, like those stating that no sides are parallel or requiring all angles to be equal, do not accurately describe a trapezium. Therefore, the choice that highlights having two opposite sides parallel while stating that the other two sides are not is the most accurate definition of a trapezium.