A polaron is a type of elementary particle.
The Dominion use phased polaron beams as their primary weapons. (DS9: "The Jem'Hadar") The ships of the Hierarchy in the Delta Quadrant are also armed with polaron-based weaponry. (VOY: "Renaissance Man")
Polaron radiation is fatal to humanoids, and has a destabilizing effect on Changeling physiology. In 2373, Starfleet Science developed modified polaron emitters which they believed would expose a Changeling. (DS9: "Apocalypse Rising")
Polarons can be used to illuminate hidden vessels. In 2371, USS Voyager used a polaron burst to bypass a Kazon-Nistrim raider's masking circuitry. (VOY: "State of Flux") In 2372, Seska located Chakotay's hidden shuttle from her raider by bouncing coherent polaron pulses from the lateral deflectors off his hull. (VOY: "Maneuvers")
When alone, the small ships of the Swarm species use polaron bursts to "paint" intruder vessels, bringing them to the attention of the larger swarm. The bursts change the shield polarity of the target ship to a rotation of 92 gigahertz, making them much more obvious to sensors. (VOY: "The Swarm")
When the biomimetic duplicate of USS Voyager was attempting to seek shelter on a Y-class planet in 2375, Tuvok suggested that a polaron burst might disrupt the shields of an intervening mining vessel long enough for them to target the warp core. However, Captain Kathryn Janeway was unwilling to destroy the other ship over a misunderstanding, even for their own survival. (VOY: "Course: Oblivion")
In 2376, the crew of Voyager considered using a polaron burst to overload the warp core of an attacking Kobali starship. However, Lyndsay Ballard rejected the proposal as she did not want the Kobali ship destroyed. (VOY: "Ashes to Ashes")