(covers information from several alternate timelines)
A temporal disruptor was a 29th century disruptor bomb, designed to demolecularize its target by fracturing spacetime. This had the effect of creating temporal distortions which grew in size and became stronger as the device destroyed its target; causing the different parts of the target to experience time at different rates and to exist in different time frames simultaneously.
Such a device was used to destroy the USS Voyager in 2372, planted aboard the ship by Captain Braxton, a 29th century Starfleet officer who held Captain Janeway and her crew responsible for his own forced retirement. Utilizing a force-3 temporal disruptor, which was designed to fracture spacetime within a radius of 150 meters, he planted the device out of phase, which precluded the possibility of the Voyager crew disarming the device through conventional means.
The disruptor was activated in 2375, resulting in a number of temporal distortions occurring throughout the ship, ultimately leading to its destruction. The timeline in which these events occurred, however, was negated when Captain Janeway and Seven of Nine were able to change history by stopping Braxton from planting the disruptor in the first place. (VOY: "Relativity")