Quantum slipstream drive is a propulsion system that pierces the quantum barrier to travel far faster than conventional warp, first encountered by Voyager aboard a disguised alien ship.
Slipstream drive creates a corridor through the quantum barrier that a ship can ride at enormous speed, but it requires precise navigational corrections, because small phase variances can destabilize the slipstream. Voyager first met the technology aboard a vessel presented as the USS Dauntless, which turned out to be a trap built by Arturis, an alien seeking revenge on the Borg.
The drive itself was real, and Voyager's crew adapted it to their own ship and attempted a long jump home. The phase variance could not be compensated in time.
As a result, in one timeline Voyager crashed on an ice planet, leaving only Chakotay and Harry Kim to survive in the Delta Flyer. Years later they sent corrected data back in time that saved the ship but prevented it from completing the journey. The drive remained a tantalizing near miss in Voyager's long search for a way home.