Antideuterium, a type of antimatter, is a quantum charged reversed form of deuterium. Antideuterium is an isotope of hydrogen which contains one antiproton and one antineutron in its nucleus, and one positron orbiting the nucleus (just as its matter opposite, deuterium, is made up of a proton, neutron, and an electron).
In a matter-antimatter reactor, such as those used in modern warp-capable starships, antimatter, such as antideuterium, reacted with normal matter. The interaction annihilated both particles and converted their mass wholly into enormous quantities of energy and a cocktail of highly energetic sub-atomic particles, which was collectively channeled by a warp drive as warp plasma. This in turn powered a warp drive, allowing the ship to travel at faster-than-light speeds.
Because of the volatility of any antimatter (it will react violently with any matter it comes into contact with, such as that which composes a standard container's walls), it was stored in specialized antimatter pods, which were surrounded by a magnetic containment field aboard a starship per SFRA 3287.0. The handling and use of this fuel had to be compliance with SFRA 4832.4.
In 2367, antideuterium was on a list of explosives that Lieutenant Commander Data and Counselor Deanna Troi searched through in an attempt to find one that could produce enough energy to release the USS Enterprise-D and an alien ship from the Tyken's Rift. (TNG: "Night Terrors")