The transwarp coil is the vital component in a Borg transwarp propulsion system. This technology allows Borg vessels to create transwarp conduits and so travel hundreds of light years in the space of a few minutes. Most Borg vessels require several transwarp coils to achieve transwarp speeds; for example, a Borg tactical cube requires at least five coils to propel it into transwarp.
The crew of the U.S.S. Voyager NCC-74656 managed to steal a transwarp coil from a Borg Sphere and successfully fitted it to their own ship. This allowed Voyager to travel 20,000 light years nearer home in little more than an hour before the device was exhausted.