An inversion wave was an energy phenomenon capable of forcing a starship into normal space via a warp field collapse, with the possible side effect of creating a time warp.
In 2372, Rom was able to create an inversion wave in the warp field of his brother's shuttle, Quark's Treasure, after it was discovered that a sabotaged command sequencer would not allow them to deactivate the warp drive. He created the wave by venting plasma from the warp core into the shuttle's cargo hold to cause a cascade reaction in kemacite being stored there. Modulating the reaction caused the inversion wave.
Although Rom's plan worked, it also had the unexpected side effect of creating a time warp, transporting the shuttle and its occupants back in time to the year 1947. Rom was later able to return all of them to their proper place in time using a reverse time warp, by using the beta radiation of an atomic explosion to trigger an inversion wave from the remaining kemacite on board the shuttle. (DS9: "Little Green Men")