Definitions of supply and taxable person clarify GST scope, registration triggers and input tax credit treatment. This Act defines core GST terms shaping levy and compliance: meanings of goods, services, supply, taxable supply, composite and mixed supply; classes of persons including taxable person, registered person, casual and non-resident taxable person; business location concepts such as place of business, fixed establishment and place of supply; and tax-accounting terms including input tax, input tax credit, reverse charge, ledgers, returns and registration-related computation of aggregate turnover.