"Cryonics" is an experimental procedure whereby patients who can no longer be kept alive with today's medical abilities are preserved at low temperature for treatment in the future. The media think of this as "freezing people," but the field is more complex than that.
Cryonics is not the same as "cryogenics," a more general term referring to a branch of physics and engineering concerned with the production of very low temperatures (e.g. by producing and storing liquid nitrogen, helium, and oxygen). See the link for "Cryotechnology."
Also included here are a few sites about "nanotechnology," a new field concerned with the manipulation of individual atoms and molecules. Cryonics researchers assume that some form of nanotechnology may be required to revive the patients preserved by cryonics techniques.