Tetryon

A tetryon is a subspace-based subatomic particle. When they hit normal space, tetryons become highly erratic and unstable.

A concentration of tetryon particles in an atmosphere could indicate a Borg presence, as typical Borg atmospheres had tetryon particles as a component. 

Several newer Starfleet starships used tetryon as part of their warp drives. This included the, and. (Star Trek: Arcadia; Star Trek: Defenders of the Federation; )

Some tools and technology using tetryon-based technology included tetryon pulse launchers and tetryon compositors. (Star Trek: Defenders of the Federation)

In 2367, the USS Prospect (NCC-60056) crew used their navigational deflector to emit a coherent graviton pulse to disperse a build-up of tetryon particles in the USS Artemis (NCC-1992)'s stardrive section. The tetryon build-up was a result of a link between normal space and the M'Tar Domain (a subspace domain).