A clapper is a device used in filmmaking that consists of two hinged wooden or plastic boards. It is commonly seen on film sets and is used to mark the start of a scene by creating a distinctive sound when the boards are brought together. The clapper is typically labeled with important information such as the scene number, take number, and production title. Its purpose is to provide a reference point for synchronizing audio and video during editing, making it an essential tool in the film industry.