(1) An opaque window that is moved in one direction to let light in and in another to close off the light. In fixed-lens cameras, one shutter often suffices for aperture and speed. In most single lens reflex (SLR) cameras, the camera has a built-in shutter that pops up to let light in and drops down after a certain amount of time, while each lens contains its own diaphragm shutter that acts like an iris to let light pass (aperture setting). See shutter speed, aperture and shutter lag.

(2) To close down an operation, project or venture.