"The process of freezing and storing the body of a diseased, recently deceased person to prevent tissue decomposition so that at some future time the person might be brought back to life upon development of new medical cures"(Dictionary).
Companies involved in cryonics describe cryonics as a way to save lives by vitrifying someone (after death) and unthawing them in the future when hopefully technology will have advanced enough to cure them of whatever disease killed them.
Many see cryonics as a way to bring people back from the dead so that they can live on until eternity. Many think of cryonics as unnatural and unpredictable.