Prison

A correctional, detention, or penal facility. 18 USC

A legal prison is the building designated by law, or used by the sheriff, for the confinement, or detention of those whose persons are judicially ordered to be kept in custody. But in cases of necessity, the sheriff may make his own house, or any other place, a prison. 2. An illegal prison is one not authorized by law, but established by private authority; when the confinement is illegal, every place where the party is arrested is a prison; as, the street, if he be detained in passing along.
   

This entry contains material from Bouvier's Legal Dictionary, a work published in the 1850's.