Tachyon

A tachyon is a type of subatomic particle that exists only at faster-than-light velocities. A tachyon cannot travel slower than light, just as many other particles cannot normally exceed the speed of light. Tachyon radiation is the radiation of energy created by these particles. Tachyons occur naturally in some star systems, such as the Bajoran system. (DS9: "Explorers") Tachyons can be detected by many types of sensors, and are emitted by certain cloaking devices. Tachyons are also sometimes indicators of time travel, and can be used to disperse certain temporal anomalies. (VOY: "Coda")

According to Silik, 22nd century Starfleet vessels had no technology which could produce tachyons on board. (ENT: "Cold Front")

In 2374, Seven of Nine attempted to modify USS Voyager's main deflector to open a transwarp conduit using tachyon bursts. However, fluctuations in Voyager's warp power caused the tachyons to build to a resonant frequency. The tachyons then flooded the warp core, threatening to cause a breach and forcing B'Elanna Torres to eject the core. (VOY: "Day of Honor")

Tachyon radiation can be associated with fluctuations in the spacetime continuum. One such incident was noted when Admiral Janeway traveled from an alternate timeline. The chrono deflector used by Janeway produced too much radiation – the admiral was protected with a dose of chronexaline. However, the device burnt itself out after one trip through time. (VOY: "Endgame")

Captain Picard used tachyon pulses at three points in time and wound up rupturing the subspace barrier and let in anti-time. However this episode is a bit of a paradox, so it is unclear as to whether or not this actually happened. (TNG: "All Good Things...") Tachyon bursts can disrupt a deflector shield, necessitating a shield harmonics reset and creating a brief window for transporter use. In 2375, Captain Jean-Luc Picard and Commander Worf attempted this tactic unsuccessfully to beam out Lieutenant Commander Data, who had malfunctioned and commandeered a Federation mission scout. Data later used tachyon bursts to disrupt the shields of Ru'afo's flagship, enabling its crew to be beamed unawares to the holoship. (Star Trek: Insurrection)