Definition of taxable supply shapes GST scope and obligations for suppliers and recipients, including composite and mixed supply. The Act defines key concepts that allocate tax incidence, compliance roles and accounting treatment: taxable supply, registered person, input tax and input tax credit; distinguishes transaction forms such as composite supply, mixed supply and continuous supplies; sets territorial markers through 'place of supply' and 'location of supplier/recipient'; and prescribes administrative and procedural terms including authorities, invoices, ledgers and returns, while cross-referencing central GST statutes for undefined terms.