Jurisdiction is the threshold question of every case: does this court have the power to hear it? The answer may turn on subject matter (a small-claims court cannot try murder), territory (courts generally reach conduct and people connected to their territory), or the parties (some tribunals bind only those a statute names).
Jurisdiction also organises whole systems. Federal countries divide it between levels of government; superior courts hold 'inherent' jurisdiction to hear anything not assigned elsewhere, while statutory courts and tribunals hold only what their statutes give them.
Sections 91 and 92 of the Constitution Act, 1867 split legislative jurisdiction between Parliament and the provinces — and a century and a half of case law referees the boundary.