A notable example of a quadrilateral that is not a parallelogram is a trapezoid (or trapezium in some regions). A trapezoid is defined as a four-sided figure with at least one pair of parallel sides. However, in contrast to parallelograms, which have both pairs of opposite sides that are parallel, a trapezoid does not meet this criterion.
To put it simply, while all parallelograms have opposite sides that are equal and parallel, trapezoids do not maintain this uniformity in their side lengths or angles. This key distinction sets trapezoids apart from parallelograms, making them a prime example of quadrilaterals that do not exhibit the properties characteristic of parallelograms.