A trimetric fracture is a breach in the spacetime continuum which can allow for passage into a region of chaotic space.

In 2375, the USS Voyager accidentally traveled through one of these fractures, becoming trapped in chaotic space. While inside, a race of aliens which resided in chaotic space managed to make contact with Commander Chakotay, by reactivating a gene causing him to experience hallucinations. Using the information transmitted to him, Chakotay was able to guide Voyager safely back to normal space. (VOY: "The Fight")