Cryonics was the science of cryogenically freezing people immediately after death or before, in the case of untreatable illnesses.
A person who was to undergo cryogenic freezing had to have all of their blood removed and replaced with cryo-preservation fluid, a very special liquid that is not particularly deeply explained in the Vorkosigan Saga. Once the tissues were perfused with the cryo-fluid, the person's body would be stored in a cryochamber where it would be brought to an extremely cold temperature.
The state of being frozen was referred to as cryostasis.
Reviving a cryogenically-frozen person, a process called cryorevival, involved reversing the steps - warm the body up, replace the fluid with blood, repair whatever damage necessitated cryo-freezing, and then provide supportive care.
A not-that-unusual side effect of being cryo-revived was cryo-amnesia. If the amnesia was not caused by serious damage to the brain, it often resolved itself after a short time in a sequence of memory cascades.
Contrast to hibernation.
Most books mention cryonics in one capacity or another. The most detailed information can be found in the following: