Cryogenic fluid
Cryogenic fluid was a type of fluid used aboard spacecraft. These fluids were stored at extremely low temperatures so that they maintained a liquid state. These fluids were used in lieu of ordinary fuel, for propulsion, because the zero gravity environment lacks the element oxygen, which creates combustion in an atmosphere.
Aboard the Galaxy-class USS Enterprise-D, in the Engineering Systems Database, there were two folders for cryogenic fluid. One of these folders was titled Cryogenic Fluid Insulation Standards and the other was titled Cryogenic Fluid Turbulence. These folders contained technical manuals relevant to the topic. (TNG: "Booby Trap", okudagram)