What is the difference between a Body Double and a Stand-In?
A body double takes the place of a main performer for certain shots in a scene where the main performer is not able to. It might be for a stunt or for a scene involving nudity. Sometimes, it is for a closeup on a hand or foot.
A stand-in is quite different. Stand-ins rarely make t into the final production. Stand-ins are usually similar height and complexion to the main performer. They are used in scene rehearsals to get the lighting and sound right before the main performer does their scene. Increasingly, stand-ins are being used for reality productions where the crew need time to calibrate their cameras and sound equipment prior to the action taking place.