Which polygon is defined as a four-sided figure with two parallel sides and two non-parallel sides?

A trapezoid is accurately defined as a four-sided polygon (quadrilateral) that has at least one pair of parallel sides. In the case of a trapezoid, while it does possess two parallel sides, the other two sides can be of any length and do not need to be parallel to each other. This characteristic differentiates specifically trapezoids from other quadrilaterals.

For example, rectangles and squares have the property that all angles are right angles, and their opposite sides are parallel and equal in length, which does not fit the criteria for defining a trapezoid. A parallelogram also has two pairs of parallel sides and equal-length sides, which conflicts with the requirement that only one pair of sides needs to be parallel in a trapezoid.

Thus, the answer correctly identifies the specific type of quadrilateral that meets the definition of having one pair of parallel sides, confirming that a trapezoid is indeed the right choice.