What does "body double" mean in the film credits?

Optical replacement refers to the polished fuselage body double. In some shots, it takes a lot of time to shoot at high altitude with the camera on the elevator frame, and the main actor certainly doesn't have time to wait for the lights, so body double is used instead of the high-speed lights of the main actor. In other scenes, such as rainy scenes and night scenes, it is necessary to adjust the lighting position repeatedly to capture the best face of the actress. For example, some people have the most beautiful 45-degree side face, and some people can add color to their faces when their hands hang down.