Cryonics refers to a super cold (usually −196°C) preservation technique that people with terminal diseases whom contemporary medicine cannot save may undertake, freezing their bodies with the hope that in a long, long time, they may be resuscitated and restored to full health with advances in medicine. Sound a little far-flung? Well there are at least a few hundred people having committed to this process.
But what does the process of suspending life actually involve? When someone reaches the point of no-return in their disease, they will be "de-animated" and cooled rapidly to a super cold temperature so as to minimize damage of body tissues. The body is then placed in liquid nitrogen to remain there until one day...in the far future.
However, there of course is a catch: the science hasn't yet figured out how to "re-animate" people. Because our cells are filled with water, when the water freezes, crystals form. And when those crystals melt...the cells in a body would simply turn to mush. Which isn't exactly the reviving of life that some people are hoping for. Nevertheless, the faith behind the technology is that by the time people are going to be unfrozen, the science will have caught up too!