The elementary particle that transmits gravitational force, manipulated by Federation technology in tractor beams, artificial gravity and deflectors, and found in nature in phenomena such as the graviton ellipse.
Gravitons are the particles responsible for gravity, and much of the everyday technology of a starship works by generating or steering them. Tractor beams, deck gravity and shield systems all depend on controlled graviton fields, and engineers often improvise graviton pulses or beams from the main deflector in an emergency.
In the Deep Space Nine episodes Favor the Bold and Sacrifice of Angels, the Dominion uses an antigraviton beam from the station's deflector array to shut down the self-replicating minefield blocking the wormhole.
The Voyager episode One Small Step features a graviton ellipse, a roaming anomaly that emerges from subspace and swallows objects in its path, including the early Mars command module Ares IV.