Which properties define a rectangle?

A rectangle is defined as a quadrilateral that possesses all the properties of a parallelogram along with the particular characteristic of having four right angles. This means that not only do opposite sides of a rectangle remain parallel and equal in length (as they do in any parallelogram), but every angle measures 90 degrees. The combination of these traits allows rectangles to maintain unique features of both parallelograms and right angles, giving them their distinct shape.

The other choices describe characteristics that do not apply to rectangles specifically, such as equal side lengths or the shape of a square. Therefore, recognizing that rectangles must adhere to both parallelogram properties and the right angles is crucial to understanding their definition.