Warp eddy
From Memory Alpha, the free Star Trek reference
A warp eddy is an emission from the warp drive of a starship such as a Danube-class runabout.
In 2369, a runabout from Deep Space 9 detected a warp eddy current in the Gamma Quadrant, believed to be from the missing USS Yangtzee Kiang. (DS9: "Battle Lines")
