Quo warranto (Latin for "by what warrant?") is one of the prerogative writs, the one that requires the person to whom it is directed to show what authority he has for exercising some right or power (or "franchise") he claims to hold.
In its earliest days in England, it might be a court's order (or "writ") to someone acting as the sheriff to prove the king had actually appointed him to that office (literally, "Who made you the sheriff?"). In the U.S.A. today, quo warranto usually arises in a civil case as a plaintiff's claim (and thus a "cause of action" instead of a writ) that some governmental or corporate official was not validly elected to that office or is wrongfully exercising powers beyond (or ultra vires) those authorized by statute or by the corporation's charter.
In some jurisdictions which have enacted judicial review statutes, such as Queensland, the prerogative writ of quo warranto has been abolished.