Voyager approaches a plasma drift.
A plasma drift was a nebula-like interstellar phenomenon.
A large plasma drift moved through the Talaxian system when Neelix was a child, blocking out the stars and moons for months. (VOY: "The Haunting of Deck Twelve")
In 2372, the USS Voyager entered a plasma drift almost half a sector long, to hide from a Vidiian-controlled star system. This was considered large for a plasma drift. Upon leaving the drift, they encountered some subspace turbulence that was in fact a divergence field. (VOY: "Deadlock")