The courts and the people who run them — particularly judges — make up the judiciary. Get caught painting graffiti on the courthouse? You just might find yourself facing the judiciary.
Another way to say judiciary is "judicial system." It's where you go with a legal dispute, whether you're divorcing someone, suing someone, or accusing someone of a crime. The Latin root is judicium, or "judgment," which is exactly the job of the judiciary: to sit in judgment of people by interpreting the law and then applying it.