Cryogenics is the study of very low temperatures or the production thereof. One application of cryogenics is cryostasis, in which lifeforms may age at a much reduced rate or experience hardly any time at all. Cryogenics is sometimes employed by pre-warp civilizations that attempt interstellar travel.
On Earth, in the late 20th century, cryogenics was a completely experimental procedure. Anyone with a seemingly incurable disease decided to get frozen so that in the future, they can be cured. To overcome the needed power source of the current century, the frozen people were placed into a solar satellite. However, it drifted out of the solar system before it was found by the USS Enterprise-D in 2364. Most of the satellite's occupants' capsules were broken and most had died, save for three others. (TNG: "The Neutral Zone")