A parallelogram is defined as what type of quadrilateral?

A parallelogram is defined specifically as a quadrilateral that possesses two pairs of parallel sides. This characteristic is what distinguishes it from other types of quadrilaterals. In essence, in a parallelogram, opposite sides are both equal in length and parallel to each other, which allows for specific properties like the equality of opposite angles and the bisection of each other by the diagonals. This definition is the foundation upon which the various properties and theorems regarding parallelograms are built. Thus, identifying a parallelogram as a quadrilateral with two pairs of parallel sides is accurate and underscores its unique geometric nature.

The other options describe different properties that do not apply to parallelograms. For instance, having only one pair of parallel sides indicates a different shape, and having four congruent sides could describe a rhombus or square but not a general parallelogram. Meanwhile, having no parallel sides would be characteristic of a trapezium or irregular quadrilateral, further emphasizing why the identification of two pairs of parallel sides is essential to defining a parallelogram.