Time Mode
A shutter setting, marked T, that opens the shutter on one press of the release and closes it on a second.
Measured in
seconds
In depth
Time mode exists so that very long exposures need no continuous pressure and no locking release, which reduces the chance of vibration. It is common on large-format and older mechanical shutters, and it survives on some digital bodies as an alternative to bulb for exposures measured in minutes or hours.
Examples in practice
Opening the shutter at dusk in T mode, walking away for twenty minutes, and closing it once the stars have registered.