A prison or penitentiary or jail (in British English, sometimes spelt gaol) is a building or system used to hold persons convicted of crimes. Many private companies in the prison industry provide services to prisons. In the US they are organized in the American Correctional Association. Their lobbying arm is ALEC which advocates legislation favorable to the industry. The practice of undergoing punishment via a prison sentence, is colloquially expressed as: "doin' time".
See also: United States prison population, United Kingdom prison population
Further Reading
List of Prisons
List of Prison Corporations