In Star Trek, a subspace shock wave is a violent compressional wave caused by a massive energy discharge which travels through the medium of subspace. These phenomena are typically created by the destruction of large planetary or stellar bodies.

In 2293, a subspace shock wave was created from the explosion and partial destruction of the Klingon moon, Praxis. The effects of the shock wave caused severe damage to Qo'noS, as well as minor damage to the nearby USS Excelsior. (Star Trek VI: The Undiscovered Country; VOY: "Flashback") The unusual supernovae caused by the Q Civil War of 2373 generated subspace shock waves. The shock waves collapsed the USS Voyager's warp field, preventing its escape and causing severe damage. (VOY: "The Q and the Grey")

Similar shickwaves also occur in the real universe, frequently as a result of supernovae. They can even been observed. In October 2002, a supernova shockwave plowing through interstellar space at 500,000 kilometers per hour was observed by the Hubble Space Telscope. This shockwave is known as the Pencil Nebula, or NGC 2736, and is part of the Vela supernova remnant, an expanding shell of a star that exploded about 11,000 years ago. Initially the shockwave was moving at millions of kilometers per hour, but the weight of all the gas it has swept up has slowed it considerably. The above region spans nearly a light year across, a small part of the 100+ light-year span of the entire Vela supernova remnant.

The explosion of a supernova expels much or all of a star's material at a velocity of up to a tenth the speed of light, driving a shock wave into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant. The expanding shock waves from supernova explosions can trigger the formation of new stars.

The three iconic pillars of cool interstellar hydrogen gas and dust that form part of the famous Eagle Nebula (also called M16), a star-forming region 6,000 light-years from Earth in the constellation Serpens, may have also now disappeared as a result of a shockwave. New data from NASA's Spitzer Space Telescope shows the pillars being scorched by an exploding star - and a shockwave has probably torn them apart. But because of the time taken for light to reach Earth from such a distance, we will not see their final destruction for 1,000 years.

The subspace shock wave was invented in Star Trek because a real shock wave traveling at sublight speeds from Praxis would have taken years to reach the Excelsior.