This is an highly advanced example of transwarp technology which generates a graviton surge, propelling a vessel into null space. During this time, the vessel can travel many hundreds or even thousands of light years.
The U.S.S. Voyager discovered a stranded alien, Tash, who was building this device as a means of getting home in a shorter period of time than he would have by other, more conventional methods.
Having helped him successfully complete and then use it to get home, Tash sent recommendations for certain modifications to the device. Following the modifications, the crew of Voyager used this device to travel across 30 sectors in less than an hour, taking 3 years off their journey home. (VGR: "The Voyager Conspiracy").