A soliton wave is a nondispersing wavefront of subspace distortion, a phenomenon which travels at faster than light speeds.
In 2368 Dr. Ja'Dar of Bilana III conducted an experiment to use soliton waves as a means of efficient faster-than-light transportation, which the USS Enterprise-D observed. The technique employed stations on two planets, one which generated the wave and one which would generate a scattering field to dissipate the wave at the destination, and in the process decelerate the vehicle traveling in it. At first the test appeared to be a success, however the unmanned test vehicle was then destroyed and the wave began to accelerate towards the destination planet, Lemma II. The wave's increased energy risked destroying Lemma, fortunately the Enterprise was able to stop it with a spread of photon torpedoes. (TNG episode: "New Ground")