Cryogenic fluid was a type of fluid used aboard spacecraft. These fluids are stored at extremely low temperatures, so that they maintain a liquid state. These fluids are 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 Installtion Standards. These folders contained technical manuals relevant to the topic. (TNG: "Booby Trap", okudagram)