A prison planet was a planet used by a species, group, or organisation as a prison.
Some prison planets resembled prisons, such as the Stormcage Containment Facility and Volag-Noc. (TV: The Pandorica Opens, The Infinite Quest) Another prison planet was Dis, used by the Imperial Landsknechte during the rule of the Earth Empire as a prison due to its proximity to a sun. (PROSE: Original Sin)
Some planets were chosen as prison planets to serve dual roles as a prison environment and sourcing a rare or useful material: New Rarga, where wompom was grown and harvested, and Raaga, a world rich in tinclavic (PROSE: Ghost Devices, TV: The Visitation), or Sarn, dumping ground for political exiles from Trion and a source of Numismaton Gas. (TV: Planet of Fire)
Shada was the prison planet of the Time Lords. (AUDIO: Shada) Inspector Thorne planned to use Urlic as a prison planet. (TV: Lost Library of Ukko) Karina Stirling spent time on the prison planet Contrelli. (COMIC: Station Zero)