The old-fashioned way of firing a camera remotely so that you don’t jog the camera by pressing the shutter button. The cable screws into a thread in the shutter release button and you push the plunger on the other end of the cable to fire the shutter. There’s a locking screw to keep the plunger pressed in for long exposures. Cable releases are rarely seen now – most cameras use wireless remote controls – though a few still have threaded shutter buttons.