Class 2 nebula
From Memory Alpha, the free Star Trek reference
A class 2 nebula is a type of nebula. The matter within the nebula is disruptive to the sensor arrays of Federation starships.
In 2376, USS Equinox crewmember Burke considered taking the ship into a class 2 nebula in order to avoid the pursuing USS Voyager. (VOY: "Equinox, Part II")
