Omicron radiation (or omicron particles) is a form of particle radiation with many applications.
Omicron radiation is dangerous to Humans; Commander Charles Tucker had to be inoculated against it when going aboard a Vissian ship whose engines generated omicron radiation. (ENT: "Cogenitor")
On the other hand, Denobulans seem to be partially immune to omicron radiation; Doctor Phlox exposed himself to it to wipe out the Borg nanoprobes invading his system. (ENT: "Regeneration") The "eels" used in Xindi biotechnology positively thrive on it, reproducing at an accelerated rate when exposed. (ENT: "The Shipment")
Omicron particles can be used to faciliate the production of antimatter; the USS Voyager attempted to recover omicron particles from a nebula to supplement its antimatter fuel reserves in 2371. (VOY: "The Cloud") Commander Chakotay was once shot down while surveying a planet with omicron particles in its atmosphere. (VOY: "Nemesis")
Yaderan holotechnology releases omicron particles. (DS9: "Shadowplay")