Subject-Matter jurisdiction is the authority of a court to hear cases of a particular type or cases relating to a specific subject matter.
Subject-Matter jurisdiction must be distinguished from personal jurisdiction, which is the power of a court to render a judgment against a particular defendant, and territorial jurisdiction, which is the power of the court to render a judgment concerning events that have occurred within a well-defined territory. Unlike personal or territorial jurisdiction, lack of subject-matter jurisdiction cannot be waived. A judgment from a court that did not have subject-matter jurisdiction is forever a nullity.
To decide a case, a court must have a combination of subject and either personal or territorial jurisdiction.
Subject-Matter jurisdiction, personal or territorial jurisdiction, and adequate notice is the three most fundamental constitutional requirements for a valid judgment.