What shape is defined as a quadrilateral with two pairs of parallel sides?

A quadrilateral with two pairs of parallel sides is defined as a parallelogram. This definition is central to understanding the properties of different quadrilaterals. A parallelogram possesses the unique characteristic that opposite sides are both equal in length and parallel, which leads to the conclusion that the opposite angles are also equal.

This foundational property is what distinguishes parallelograms from other types of quadrilaterals. While rectangles and squares can also be classified under the broader category of parallelograms, they possess additional specific characteristics, such as having right angles (in the case of rectangles) or equal sides (for squares). For example, although all squares are parallelograms, not all parallelograms are squares. Similarly, trapezoids, which have only one pair of parallel sides, do not share the same defining attribute. Therefore, the term "parallelogram" accurately encompasses the broader class of shapes that meet the criteria of having two pairs of parallel sides.