A subspace field was an enveloping projected-energy phenomenon which could be produced by warp-powered starships and other technology designed to distort space.
In 2369, Deep Space 9 Chief of Operations Miles O'Brien was able to modify the subspace field output of the station's deflector generators enough to create a low-level subspace field around the station. This had the effect of reducing the station's inertial mass enough to allow the station's thrusters to move it from Bajor to the mouth of the Bajoran wormhole, enabling Bajor to stake a claim to the wormhole before the Cardassians could. (DS9: "Emissary")
The sensors of a USS Enterprise-D runabout were unable to get through a subspace field caused by a temporal fragment. (TNG: "Timescape")
Subspace field emitters were a component of starships. (DS9: "The Homecoming")
If a high-energy output was used in the generation of a subspace field, it could be used to jam sensors. (TNG: "The Wounded")