Cryonics is the low-temperature preservation of humans an other animals that can no longer be sustained by contemporary medicine until resuscitation may be possible in the future. Human cryopreservation is not currently reversible. In the United States, cryonics can only be legally performed on humans after pronounced legally dead. The rationale for cryonics is that the process may be reversible in the future if performed soon enough, and that cryopreserved people are not dead by the modern information-theoretic definition of death. Cryonics is derived from the Greek word κρύος (kryos), meaning cold.