Short for stock keeping unit, SKU is a unique numerical identifying number that refers to a specific stock item in a retailer's inventory or product catalog. The SKU is often used to identify the product, product size or type, and the manufacturer.In the retail industry, the SKU is a part of the backend inventory control system and enables a retailer to track a product in their inventory that may be in warehouses or in retail outlets. See also UPC.PREVIOUSskin.he SKU is often used to identify the product, product size or type, and the manufacturer. In the retail industry, the SKU is a part of the backend inventory control system and enables a retailer to track a product in their inventory that may be in warehouses or in retail outlets. See also UPC. PREVIOUSskin.