A quantum singularity is a term used in Star Trek to refer to a point or region in the space-time continuum where normal physical models do not apply and extraordinary amounts of gravitational forces are typically present. Singularities can be both natural and artificial: wormholes, quantum matrices of planets, and black holes all can contain singularities, as do certain reactors (e.g. those found in Romulan starships).

There are relationships between singularities and time. Singularities in general, and quantum singularities in particular, are known by 24th century science even when stable to send out waves of temporal displacement that affects, among other things, delta-series radioisotopes. The USS Enterprise encountered temporal effects from a singularity in a black star in 2267. (TOS: "Tomorrow is Yesterday") Also, energy emitted by an exploding microscopic singularity can shift chroniton particles into a high state of temporal polarization and/or create "bubbles" in subspace. This latter result can cause temporal anomalies and was directly observed by the USS Defiant in 2371. (DS9: "Past Tense, Part I"). In 2371, the USS Voyager, while traveling in the Delta Quadrant, became trapped in a type-4 singularity. (VOY: "Parallax").

Singularities can be detected by the effect they have on local gravimetric field signatures nearby (although they can be buried so far down in subspace layers that they cannot be detected in that way), and/or by using tetryon emissions as a guide.One example of the use of a singularity was demonstrated in 2373. The Borg, Species 8472, and the USS Voyager were all able to travel between the fluidic space dimension and our dimension via artificially created quantum singularities. (VOY: "Scorpion", "Scorpion, Part II").

The term quantum singularity used in Star Trek actually resembles what the real scientific calls a gravitational singularity - massive, localized distortions of space and time. A gravitational singularity (sometimes spacetime singularity) is, approximately, a place where quantities which are used to measure the gravitational field become infinite. Such quantities include the curvature of spacetime or the density of matter. More accurately, a spacetime with a singularity contains geodesics ("straight lines" to curved spacetime) which cannot be completed in a smooth manner. The limit of such a geodesic is the singularity.

The two most important types of spacetime singularities are curvature singularities and conical singularities. Singularities can also be divided according to whether they are covered by an event horizon or not (naked singularities). According to general relativity, the initial state of the universe, at the beginning of the Big Bang, was a singularity. Another type of singularity predicted by general relativity is inside a black hole: any star collapsing beyond a certain point would form a black hole, inside which a singularity (covered by an event horizon) would be formed, as all the matter would flow into a certain point (or a circular line, if the black hole is rotating). These singularities are also known as curvature singularities.