(covers information from several alternate timelines)
A temporal shock wave, also known as a spacetime shock wave or a temporal wavefront, is a powerful buildup of temporal energy which travels through space, changing history as it propagates, a wave front in the fabric of spacetime.
In an alternate timeline, a Krenim weapon ship, constructed by a scientist named Annorax, produced temporal shock waves as byproducts of the temporal incursions it initiated. When the weapon ship eliminated an object from history, a resultant shock wave radiated from the point of the incursion, and altered the timeline of the universe to compensate for the absence of the object from history. This timeline was later negated when, as a result of massive battle damage, a temporal incursion was initiated within the weapon ship itself, reaulting in a shock wave that erased it and all of the damage it did to the timeline from history. (VOY: "Year of Hell", "Year of Hell, Part II")