Clapperboard

A clapperboard, also known as a slate, is a device used during film production. It has two parts which are hinged together similar to a small collapsible clapboard. One part of it is a rectangular board with the movie’s name, scene and take number written on it. The other part has a small arm that can be flipped open and closed, and it makes a loud clapping noise when it is shut.

When making a film or video, the clapperboard is held in front of the camera to begin each new shot. The person holding the clapperboard announces the scene and take number for the camera and then they clap the board shut. The sharp sound of the board serves as both a visual and an audio cue that helps video and sound editors to match up the appropriate footage and audio tracks later on.

It's just like when we are playing a game, and when we finish one level, we close the book and start a new one. In movies, they need to tell everybody that they are starting a new level, and they make an extra loud sound so that everybody knows when it happened.