Interpretation of service descriptions: prefer specific descriptions; classify bundled services by essential character or highest-liability rule. The provision treats services used to provide a referenced main service as separately assessable input services and mandates that the most specific description governs where descriptions differ. For bundled services, if elements are naturally bundled the bundle is classified by its essential character; if not naturally bundled, classification favors the single service that yields the highest service tax liability. A bundled service combines elements of one or more services.