The Moment

Mentioned only by The Partisan as a device that the Doctor used to end the Last Great Time War, destroying Gallifrey, the invading Dalek forces, and the Time Lords, all in a second.

Presumably, given the device's name, this may also be the device that created the time lock that bound the Last Great Time War from anyone who might be tempted to travel back in time to any point during its duration and tamper with its events.