Rectangle

A rectangle is a four-sided polygon with four right angles, whose opposite sides are parallel and are equal.

A rectangle is a particular sort of parallelogram, but can't say that all parallelograms would be rectangles, because a rectangle is a shape where opposites sides are parallel and all the corners are 90 degree angles. Some parallelograms would be rectangles, but not all.

Area of a rectangle
The area of a rectangle is the product of its width and length.