Cryotanks are generally a means of preserving organics, dead or alive, for long periods of time.
Cryotank or cryogenic tank is a tank that is used to store frozen biological material
Cryotank is mentioned by Stephenie Meyer in the novel The Host . It is supposed to be a container to preserve the sensitive souls . The souls can not survive long without this in any planet except Origin . Origin is their first planet and the only one planet where 'the souls can live outside of a host for very long.'
This tank is also known as hybernation tank and is used to carry the souls from one planet to another. The souls came to a planet with spaceships and they are kept in hybernation mode there. The known souls who are mentioned in the novel specifically, to be kept in it are - Wanderer, The Seeker, Sunlight Passing Through the Ice and Summer .
- Cryonics on Wikipedia
In science fiction, it is used to freeze people. (cry- is a Greek prefix which means "cold or freezing") So people are stored in the tank frozen to come out in the future. Cryotanks are found in some science fiction films such as Prometheus (2012) and The Host (2013).
Cryotank on Wookieepedia