A jailbird is someone who's been in prison or is still there. Your parents might refer to your disgraced car thief cousin a jailbird.
Jailbird is a casual and derogatory term for a convicted criminal, especially one who's been in and out of jail several times. Following a prison escape, a local newspaper's headline might read "Jailbird on the Loose!" Jailbird, coined in the 17th century, equates the image of a bird in a cage with a prisoner in jail.