Wormhole
A wormhole was a "tunnel" connecting two separate points in space-time. It consisted of two apertures in space-time connected by a conduit outside normal space, through subspace. Since this conduit was shorter than the distance between the two points in normal space, it allowed rapid travel between the two points.

A wormhole was described as a time-space disturbance or as a space-time distortion. () It was described, as well, as a space-time anomaly. (; )

A tetryon scan of a wormhole would typically show up neutrinos, ionized hydrogen, theta-band radiation, and would certainly have to show quantum level fluctuations. ()

If a wormhole was large and stable enough, a starship (or other traveler) could travel through it. A wormhole could also connect two different points in time as well. As wormholes age they collapse, becoming smaller and are known as micro-wormholes. ()

Before knowing where the Harry Kim wormhole ended, Tuvok stated that there was a 75% chance that it didn't lead to the Alpha Quadrant. ()

Natural wormholes
Quantum singularities could act as wormholes. When Voyager 6 fell into a quantum singularity, at the time called a black hole, and reemerged in an unknown region of space, speculated by Captain Decker to be the "far side" of the galaxy. There it landed on a planet of sentient machines, and became V'ger. ()

Wormholes and the possibility of using them for time travel had been recognized by Human scientists since the 20th century. In 2368, Captain Jean-Luc Picard of the  agreed with faux historian Berlinghoff Rasmussen that using knowledge gained by means of time travel through a wormhole (for example, in order to save an endangered planet) could allow the "next Adolf Hitler" or Khan Noonien Singh to come into being. According to the captain, first year philosophy students had been asked the question ever since the first wormholes had been . ()

Small and extremely unstable wormholes have been mapped near 39 T-Tauri systems in the century preceding 2367, and more before. That year, Data claimed that he had passed through three unstable wormholes during his time with Starfleet. Wormholes of  small size and relatively short period would typically be local phenomenon rather then galaxy-spanning. ()

No known naturally-occurring stable wormholes had yet been discovered in the Alpha or Beta Quadrants. The only likely candidate, the Barzan wormhole, was found to be unstable at its far terminus. However, several relatively stable wormhole-like phenomena had been reported in the Delta Quadrant. (; )

It was believed possible for wormholes to just form suddenly, and a newly-formed one might be known as a "baby wormhole". ()

The transwarp conduits used by the Borg were believed to be wormholes. ()

In the 32nd century, there was a natural wormhole one hundred light years from the planet Hima. ()

Artificial wormholes

The only known stable artificial wormhole was the Bajoran wormhole, created by beings known to the Bajorans as the Prophets, who dwelled within. This wormhole was stable enough for long-term, two-way space travel between the Bajor system in the Alpha Quadrant and the Idran system in the Gamma Quadrant. ()

In the alternate 2259, the Federation was engaged in wormhole research. The location of the research site was labeled on a map depicting a section of the Alpha Quadrant. This map was seen on a powerwall in the offices of Admirals  and  at Starfleet Headquarters. ()

In the 2370s, the Federation investigated methods of creating artificial wormholes. The project was headed by Dr. Lenara Kahn of the Trill Science Ministry, who eventually developed a workable theory that she tested aboard the  in 2372. The technique involved generating a subspace tensor matrix in the 25,000-30,000  range, and then sending out a magneton pulse using a target drone. The pulse would then interact with the matrix to produce a subspace distortion, which would become an opening in the space-time continuum.

The first test of this technique produced a wormhole that was stable for 23.4 seconds. On the second test, a class-4 probe was launched through the wormhole to simulate the passage of an interstellar spacecraft. However, the probe's shields unexpectedly interacted with the tetryon field, collapsing the wormhole and producing a massive graviton shock wave that heavily damaged the Defiant. ()

The MIDAS array was able to create an artificial micro-wormhole that connected the Alpha Quadrant to the Delta Quadrant, but it was only stable for a brief moment. ()

According to a classroom chart in Keiko O'Brien's school aboard Deep Space 9, "Most wormhole are naturally occurring or the result of dangerous warp drive malfunctions. Such wormholes tend to oscillate wildly across time and space, making them useless for normal interstellar commerce." () Such an imbalance happened to the  during the 2270s, when Captain Kirk ordered the ship's warp drive utilized before proper simulations had been completed, causing the Enterprise to become trapped in a wormhole for a brief period of time. The crew survived the wormhole effect after Commander Will Decker ordered Lieutenant Pavel Chekov to fire a photon torpedo at an asteroid that had been pulled in with them. () 

In theory, detonating a heavy gravimetric charge in a Type-6 protostar could open up a wormhole to a given location. ()

Background information
André Bormanis commented: "The wormhole was a really interesting, fascinating moment in Star Trek: The Motion Picture and so we knew that that would be a fun idea to revisit it in later series. It became the benchmark of Deep Space Nine and it is a really intriguing idea that the fans have very much responded to. With our warp drive we can travel from here to the next nearest star in a couple of days. But the wormhole gave us the opportunity to travel 50,000 light years, half the breadth of the galaxy, in a matter of seconds. That was an astonishing thing, even for our 24th Century characters"

List of wormholes
 Bajoran wormhole
 Barzan wormhole
 Cyclic wormhole
 Interspatial flexure
 Intermittent cyclical vortex
 Micro-wormhole
 Harry Kim wormhole
 Möbius Inversion
 Spatial vortex

See also
 Spatial gradient
 Subspace axis
 Subspace instability
 Subspatial contortion
 Temporal variance
 Transkinetic vector
 Wormhole effect
 Geodesic fold

External links
 
 

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Time travel
Transwarp
Wormholes