What Do We Mean by a Shutter and How Is It Used in Photography?

In a camera the shutter is the mechanism which controls the length of time the camera sensor or film is exposed to the light entering through the lens. When the shutter button is pressed by the photographer the shutter opens for the amount of time set in the cameras exposure settings. When the shutter is open the camera sensor or film are exposed to light which is captured to produce an image. Open the shutter for too long and the image will be over exposed, open it for too little time an the image will be under exposed.