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Parralelogram ○꠹｜Definition｜1st｜20251119205401-00-⌔
Parallelogram
In Euclidean geometry, a parallelogram is a chiral simple (non- self-intersecting) quadrilateral with two pairs of parallel sides. The opposite or facing sides of a parallelogram are of equal length and the opposite angles of a parallelogram are of equal measure. The congruence of opposite sides and opposite angles is a direct consequence of the Euclidean parallel postulate and neither condition can be proven without appealing to the Euclidean parallel postulate or one of its equivalent formulations.
By comparison, a quadrilateral with at least one pair of parallel sides is a trapezoid in American English or a trapezium in British English.
The three-dimensional counterpart of a parallelogram is a parallelepiped.
The word “parallelogram” comes from the Greek παραλληλό-γραμμον, parallēló-grammon, which means “a shape of parallel lines”.
Printed 2026-06-28.
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