Cable Release
A mechanical or electronic remote that fires the shutter without the photographer touching the camera.
In depth
Pressing a shutter button transmits enough movement to blur a tripod exposure in the vulnerable range around a quarter of a second. A release removes that entirely, and a locking version is required for bulb exposures. Where no release is available, a two-second self-timer achieves much of the same effect.
Examples in practice
A locking cable release holds the shutter open for a four-minute star exposure without any hand contact.