A rectangle is a four-sided plane figure, or any quadrilateral, with four right angles. Opposite sides of a rectangle are parallel and equal in length.
Diagonal lines that are drawn through a rectangle from corner to corner are equal in width. A square is technically a rectangle with four equal sides. The dual polygon of a rectangle is a rhombus.
The word rectangle comes from the Latin word "rectangulus", which translates to "right angle". All rectangles have a length, width, perimeter and area. A rectangle is a special type of parallelogram, and a parallelogram is a special type of trapezoid.