En geometría plana, un rectángulo es un paralelogramo cuyos cuatro lados forman ángulos rectos entre sí. Los lados opuestos tienen la misma longitud. El perímetro de un rectángulo es igual a la suma de todos sus lados. El área de un rectángulo es igual al producto de dos de sus lados contiguos.

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In Euclidean plane geometry, a rectangle is a quadrilateral with four right angles. It can also be defined as an equiangular quadrilateral, since equiangular means that all of its angles are equal (360°/4 = 90°). It can also be defined as a parallelogram containing a right angle. A rectangle with four sides of equal length is a square. The term oblong is occasionally used to refer to a non-square rectangle.A rectangle with vertices ABCD would be denoted as ABCD. The word rectangle comes from the Latin rectangulus, which is a combination of rectus (right) and angulus (angle). A crossed rectangle is a crossed (self-intersecting) quadrilateral which consists of two opposite sides of a rectangle along with the two diagonals.It is a special case of an antiparallelogram, and its angles are not right angles. Other geometries, such as spherical, elliptic, and hyperbolic, have so-called rectangles with opposite sides equal in length and equal angles that are not right angles. Rectangles are involved in many problems, such as tiling the plane by rectangles or tiling a rectangle by polygons.

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