A yardbird is a prisoner — an American slang word, and old-fashioned now. The picture behind it is the prison yard: the fenced open space where prisoners are let out to walk, and a man in there is like a bird in a cage, moving around in a small square of open air. It usually suggests someone who has been inside a long time, someone who belongs to that yard. This is very informal, and it belongs mostly to mid-20th-century American speech, crime novels, and blues and jazz talk; a modern newspaper would write "inmate" or "prisoner". During the Second World War it meant something else: a new, untrained soldier, the kind who gets given the dull jobs. That military sense has almost disappeared. Students may also have met the name in music — the jazz player Charlie Parker was nicknamed Yardbird, or Bird, and there was a British band called the Yardbirds.

（美式俚語）囚犯、蹲苦窯的人