A rectangular expansion joint is a type of joint that is used to absorb the thermal expansion and contraction of two structures that are connected together. It is typically used in applications where the structures are connected by a rigid connection, such as a concrete wall or a steel beam. The joint is designed to allow the two structures to move independently of each other without causing any damage to the connection. It is commonly used in bridges, buildings, and other structures that need to be able to accommodate movement due to temperature changes.