Tax treaty definitions clarify residency, company, competent authority, international traffic and fiscal year for cross-border taxation. Article 3 defines key terms for the India-Switzerland DTAA: the territorial scope of India and Switzerland; 'Contracting State'; 'person', 'company' and 'enterprise' for determining taxable entities; each State's competent authority; 'national'; the meaning of international traffic and 'operation of aircraft' as commercial air transport activities; and the treaty-specific definitions of 'fiscal year'. It further provides that undefined terms take their meaning from the domestic law of the applying Contracting State, and notes textual substitutions to certain definitions.