Transwarp drive was an experimental Federation propulsion system intended to push starships far beyond conventional warp speeds, tested aboard the Excelsior and later in shuttle experiments.
Starfleet built the USS Excelsior as the testbed for its transwarp programme in the 2280s, promoting it as the next great leap in propulsion. Before the ship could pursue the stolen Enterprise, Montgomery Scott quietly removed components from its drive, leaving the prototype stranded in spacedock.
The Federation's later transwarp research focused on breaking the warp 10 barrier. In the 24th century Voyager's crew developed a modified shuttle using a new form of dilithium, and Tom Paris piloted it to the threshold of infinite velocity. The flight succeeded briefly but caused severe mutations in Paris, and the approach was abandoned.
The Borg used a separate form of transwarp travel based on a network of conduits, which Federation engineers studied but never fully mastered. Voyager later acquired and briefly used a Borg transwarp coil, though it was soon exhausted.