From Longman Dictionary of Contemporary Englishopen prisonˌopen ˈprison noun [countable] British English SCJa prison that does not restrict the freedom of prisoners as much as ordinary prisons
Examples from the Corpus
open prison• Visits to Parliament and an open prison have given them insights into less accessible subjects.• He turned out to have escaped from an open prison in Dorking.• Goulais is now in an open prison, where he enjoys special treatment.• If anyone deserved a few years in an open prison it was Beamish.• Successful inmates can hope to move back to a lower category C security, or even a Category D open prison.• She was picked up outside the gates of Askham Grange open prison near York by her son and daughter.• He should have returned to the open prison on the tenth of August. 