The
privilege granted to the
United States Supreme Court to pass
judgement on whether the
laws passed by
Congress are
constitutional. It also allows for judging the actions of the
president against the
Constitution.
It's origin is generally attributed to John Marshall though ideas similar to it had be incorporated in other democratic governments (most notably England when reviewing colonial law.)
It is now considered to be part of the normal system of checks and balances of democratic government though the United States is one of the few that uses it frequently.