Tax treaty definitions determine residency, taxable persons, and scope, clarifying treatment and applicability of taxes under the DTAA. Article 3 sets definitional rules for the Agreement, defining territorial scope and key terms such as company, person, national, tax, enterprise of a Contracting State, fiscal year, international traffic, and competent authority. It specifies that a company includes entities treated as such under domestic tax law, that tax means Indian or Singapore tax but excludes penalties and default-related amounts, and that undefined terms adopt their meaning under the domestic law of the applying Contracting State unless context dictates otherwise.