A chamber or field that suspends a living body's processes, used in Star Trek to preserve the sick, to protect crews from danger and for long journeys.
Stasis units hold a person in suspended animation without the ageing that comes with ordinary sleep. They descend from the cryogenic sleeper ships of the 20th and 21st centuries, such as the SS Botany Bay in Space Seed, and are used in sickbay to keep a patient alive until treatment is possible.
Star Trek: Voyager makes much use of them. In The Thaw the crew find survivors of a planetary disaster who have lain in stasis for years, their minds joined in a virtual world ruled by a clown. In One, the whole crew must sleep in stasis chambers for a month to cross a nebula, leaving Seven of Nine and the Doctor to run the ship.
Stasis fields are also used to store biological samples, dangerous organisms and the dead. The cryotubes that hold Khan's followers in Star Trek Into Darkness serve the same purpose.