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 ; or a parallelogram containing a right angle. A rectangle with four sides of equal length is a square. The term "oblong" is used to refer to a non-square rectangle. A rectangle with vertices ABCD would be denoted as  ABCD.

ऐसा चतुर्भुज जिसके चारों अन्तःकोण समकोण हों उसे आयत (Rectangle) कहते हैं। आयत एक ऐसा चतुर्भुज है जिसकी आमने सामने की भुजाएं समांतर होती है, "आयत" कहलाता है।