A rectangle is a four-sided shape, known as a quadrilateral, with opposite sides that are equal in length. Each of the four angles in a rectangle measures 90 degrees, making it a type of parallelogram. Rectangles can vary in size, but they always maintain these properties. Rectangles are commonly found in everyday life, such as in books, screens, and tables. The area of a rectangle can be calculated by multiplying its length by its width, while the perimeter is found by adding the lengths of all four sides.