An open prison (open jail) is an informal description applied to any penal establishment in which the prisoners are trusted to serve their sentences with minimal supervision and perimeter security and are not locked up in prison cells. Prisoners may be permitted to take up employment while serving their sentence. In the UK, open prisons are often part of a rehabilitation plan for prisoners moved from closed prisons. They may be designated "training prisons" and are only for prisoners considered a low risk to the public.