A meson is a sub-atomic, non-elementary particle composed of an even number of quarks and anti-quarks.
All mesons are unstable and fluctuations in the meson field were observed at the terminus of the Barzan wormhole, creating instability in the wormhole and causing its terminus to shift between the Delta Quadrant and the Denkiri Arm of the Gamma Quadrant. (TNG: "The Price")
While scanning for the crash landed runabout USS Yangtzee Kiang in the Gamma Quadrant, Lieutenant Jadzia Dax noted that the warp eddy had traces of meson particle emissions, which made it a Starfleet power reactor. (DS9: "Battle Lines")