A neutrino cloud was an astronomical object composed of neutrinos, that generated an electromagnetic field. It normally went undetected by 2370s Federation sensors.
The harmonic resonance of the neutrino cloulds around Rosseau V occasionally became synchronous, causing sounds similar to music. (TNG: "The Dauphin")
In 2376, Harry Kim gave a neutrino cloud as a possible cause for a graviton ellipse's changes in course. (VOY: "One Small Step")