The Defiant in front of the Bajoran wormhole and a subspace inversion of it
A subspace inversion is an inversion in the subspace field.
In 2371, a carrier wave emitted by the wormhole relay station created a subspace inversion in the Bajoran wormhole, causing an increase in the pull of its gravity well. (DS9: "Destiny")
In early 2372, the wormhole underwent a natural subspace inversion like in all fifty years. (DS9: "The Visitor")
In an alternate timeline, the USS Defiant was damaged by the inversion, which pulled Benjamin Sisko out of the normal space-time continuum. He would only reappear when the wormhole underwent an inversion. In 2422, Jake Sisko, Captain Nog, Jadzia Dax and Julian Bashir brought the Defiant to the wormhole during an inversion to rescue the captain, but they were unsuccessful. (DS9: "The Visitor")
After the conception of Q Junior in 2373, Q noted that he could no longer cause temporal anomalies or spatial inversions if he wanted to be a good role model. (VOY: "The Q and the Grey")