What is a plane figure that has four sides, two of which are parallel?

A plane figure that has four sides, with two of those sides being parallel, is specifically known as a trapezoid. The defining characteristic of a trapezoid is the presence of at least one pair of parallel sides, distinguishing it from other four-sided figures like rectangles and squares, which have two pairs of parallel sides.

While rectangles and squares both fit the criteria of having four sides, they are defined by having two pairs of parallel sides and right angles. A quadrilateral is a broader category that encompasses any four-sided figure, which includes rectangles, squares, trapezoids, and more. Therefore, the trapezoid is the most accurate answer for a figure that meets the specific condition of having one pair of parallel sides.