In Star Trek, a tetryon is a subatomic particle that can only exist naturally in subspace environments. Tetryon radiation is a bombardment of these particles. Since these particles are a property of subspace, they become highly energetic and unstable when they are extruded into normal space, which can occur by both natural and artificial means. Tetryons have a random momentum, and thus cannot be tracked by sensors.

Tetryons were first mentioned in TNG: "Schisms". Solanagen-based lifeforms from a tertiary subspace manifold used a stream of spatially inverted tetryons to open a spatial rupture between their native realm and the USS Enterprise-D. This allowed them to abduct several Enterprise crew members for experimentation. Intense tetryon fields, such as those surrounding the Hekaras Corridor, pose a hazard to spacecraft. (TNG: "Force of Nature")

In 2372, tetryon pulse echos were used to navigate the highly unstable atmosphere of a gas giant. However, course modifications were required after each pulse in order to avoid detection. This meant that the random momentum to avoid being tracked by sensors was invalid when emitted as a pulse. (DS9: "Starship Down"). Later, USS Voyager traveled through a region of heavy tetryon radiation. Lieutenant Tuvok enhanced the ship's shields to compensate. (VOY: "Distant Origin"). The atmosphere inside a Borg cube contains tetryon particles. (VOY: "Infinite Regress")

The energy barrier that isolates the territory of the Ventu on Ledos has a distinct tetryon signature. The Borg had previously encountered the technology in Species 312. The barrier left a distinct tetryon flux on debris from a Voyager shuttlecraft that crashed into it in 2377. (VOY: "Natural Law").

As teryons are prevalent in subspace, the closest equivalent to these particles in real Physics are probably fermions - Petit and Sarrazin pointed out that their theory on 'subspace' only works for fermions. Fermions are particles of matter which are characterized by spin in odd half-integer quantum units (1/2,3/2,5/2...). Fermions were named by Paul Dirac in 1947 after the Italian physicist Enrico Fermi. They obey the Pauli exclusion principle and have antisymmetric wavefunctions. All observed elementary particles are either fermions or bosons. The known elementary fermions are divided into two groups - quarks and leptons. Quarks make up protons, neutrons and other baryons, which are composite fermions; they also comprise mesons, which are composite bosons. Leptons include the electron and similar, heavier particles (the muon and tauon); they also include neutrinos.