What is Subject Matter?

Legal Definition
The cause, the object, the thing in dispute.

2. It is a fatal objection to the jurisdiction of the court when it has not cognizance of the subject-matter of the action; as, if a cause exclusively of admiralty jurisdiction were brought in a court of common law, or a criminal proceeding in a court having jurisdiction of civil cases only. 10 Co. 68, 76 1 Ventr. 133; 8 Mass. 87; 12 Mass. 367. In such case, neither a plea to the jurisdiction, nor any other plea would be required to oust the court of jurisdiction. The cause might be dismissed upon motion, by the court, ex officio.
-- Bouviers Law Dictionary
Legal Definition
the name that is given to the matter that is in dispute.
Legal Definition
The thing in controversy or the matter spoken or written about.
-- Black's Law Dictionary