Tax treaty definitions determine residency, company status, immovable property and competent authority for cross-border taxation. This provision defines territorial scope, persons, companies, nationals, enterprises, international traffic, immovable property, competent authority, fiscal year and the term 'tax' for the Convention. It treats 'person' and 'company' by reference to taxable units under domestic law, defines immovable property by the law of the State where situated with specified inclusions and exclusions, identifies competent authorities for administrative cooperation, and provides that undefined terms take their domestic law meanings when applying the Agreement.