Salusa Secundus - Dune

In "Terminology of the Imperium," the glossary of the 1965 novel Dune, Herbert writes:

SALUSA SECUNDUS: third planet of Gamma Waiping; designated Imperial Prison Planet after removal of the Royal Court to Kaitain. Salusa Secundus is homeworld of House Corrino, and the second stopping point in migrations of the Wandering Zensunni. Fremen tradition says they were slaves on S.S. for nine generations.

The Padishah Emperors of the known universe use Salusa Secundus as a prison planet, a penal colony where the "worst riff-raff in the galaxy are sent." Infamously known as a "hell world," the planet's climate is so severe that the "mortality rate among new prisoners is higher than sixty per cent." In the events of Dune it is also revealed that the Imperial House Corrino makes use of the planet as a secret recruiting and training ground for its fierce Sardaukar troops. After Paul Atreides ascends to the Imperial Throne, House Corrino is exiled to Salusa Secundus, with the exception of Padishah Emperor Shaddam IV’s eldest daughter, Princess Irulan, who is married to Paul.