Warp frequency

A warp frequency is a unique and detectable phenomenon related to the generation of a warp field. Normal dilithium destabilizes at extremely high warp frequencies, a fact which limited the maximum warp speed of most warp-capable vessels. If a vessel's specific warp frequency was known, it made a specific ship much easier to find with sensors. 

In 2152, Captain Archer was able to convince Firek Plinn, a Retellian pirate, to reveal the warp frequency of his ship, allowing Enterprise to locate his brother, Firek Goff, who had kidnapped Commander Tucker and Kaitaama, a Kriosian princess. 

In 2372, the crew of the USS Voyager discovered a new form of dilithium in an asteroid field in the Delta Quadrant, which remained stable at a much higher warp frequency than normal dilithium. By utilizing this dilithium, the crew was able to construct a prototype transwarp drive aboard their shuttlecraft Cochrane, which Tom Paris used to cross the warp 10 threshold. Doing so, however, caused unexpected physiological side effects, and the technology was subsequently abandoned.