Other forms: shutters; shuttered; shuttering
A shutter is a solid window covering that you close to block out light and open to let the sun shine in.
Long ago, most houses had outdoor shutters that acted as an old-fashioned security system, as well as protection from sunlight and stormy weather. Many modern homes have decorative shutters that don't actually open and close. There's another kind of shutter inside your camera, which also opens and closes to let light through to capture a photographic image. Shutter dates from the 1720s, when it was short for window-shutters.