Judicial review

The power of judicial review is the authority of the federal courts to say what the law is. Chief Justice Marshall established this doctrine in Marbury v. Madison:

It is emphatically the province and duty of the judicial department to say what the law is.

If, for example, a law is unconstitutional, then courts should not enforce it.

This is not to be confused with additional unjustified power taken by the judiciary for itself that is known as judicial supremacy or judicial activism.