A rectangle is a four-sided shape, known as a quadrilateral, with opposite sides that are equal in length. It has four right angles, each measuring 90 degrees. The length and width of a rectangle can vary, but the defining characteristic is that the opposite sides are parallel and equal. Rectangles are commonly found in everyday objects, such as 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 together the lengths of all four sides.