BIW (Body in White) fixture is a tool used in the automotive industry for assembly line production of car bodies. It is a specialized jig used to hold and position different components of the car body, such as the doors, hood, and roof, in their exact location during the welding and assembly process. This ensures that the car body is assembled accurately and consistently, according to the design specifications. BIW fixtures are custom-made for each car model and are an essential tool for efficient and precise production of car bodies.