Cryonics is the practice of freezing clinically dead people in liquid nitrogen with the hope of future reanimation. Advanced nanotechnology or mind uploading are the favored prospects for implementing the "and then a miracle occurs" stage, which is currently everything that follows the initial freezing.
Scientists will admit that some sort of cryogenic preservation and revival does not seem to violate known physics. But they stress that, in practical terms, freezing and reviving dead humans is so far off as to hardly be worth taking seriously, and present cryonics practice is speculation at best and quackery and pseudoscience at worst.
Nevertheless, cryonicists will accept considerable amounts of your money right now for procedures based only on vague science-fiction-level speculations, with no scientific evidence whatsoever that any of their present actions will help achieve their declared aims. They sincerely consider this an obviously sensible idea that you would have to be stupid not to sign up for.