behind bars behind bars {adv. phr.} In jail; in prison. He was a pickpocket and had spent many years behind bars. That boy is always in trouble and will end up behind bars. Categories: add yours {adv. phr.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2025 To section: B Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Add my comment