Advance ruling clarifies GST applicability for suppliers, specifying the authority, applicant status, and appellate review process. Definitions specify that an advance ruling is a decision by the Authority or Appellate Authority on questions related to the supply of goods or services proposed or undertaken by an applicant; the Authority and Appellate Authority are the bodies constituted to render and review such rulings; 'applicant' means a person registered or seeking registration under the Act; and 'application' means an application made to the Authority under the relevant provision.