**A rectangle is a quadrilateral that has four sides.** In a rectangle, the opposite sides are of equal length and also parallel. Because of this, a rectangle is also a parallelogram.

This four-sided shape has four angles that are right angles, or are 90 degrees each. The sum of the interior angles of a rectangle is 360 degrees. Its two diagonals are equal and intersect at the center of the rectangle.

Some important formulas associated with rectangles are area, perimeter and diagonal lengths. A rectangle has a length and a width, and the area formula is length multiplied by the width, or l x w. The perimeter is given as 2(l +w), and the diagonal length is found by taking the square root of the sum of the squares of the width and lengths, respectively.