(1) An organization or an individual that enters into an agreement with the acquirer for the supply of a product or a service. (ISO/IEC 2015)
(2) Suppliers may be internal or external. (ISO/IEC 2015)
(1) and (2) ISO/IEC/IEEE. 2015. Systems and Software Engineering -- System Life Cycle Processes. Geneva, Switzerland: International Organisation for Standardisation / International Electrotechnical Commissions / Institute of Electrical and Electronics Engineers. ISO/IEC/IEEE 15288:2015.