GTIN simply means Global Trade Item Number and can refer to a number of barcode types. For example an EAN-13, UPC-A, EAN-8 or ITF-14 are all considered to be GTINs. GTINs are globally unique numbers that are assigned to retail products or logistics units used in warehousing. When a barcode is assigned to a product it can be tracked from the warehouse, through wholesalers and eventually scanned at POS in retail outlets. The barcoding system allows companies to keep track of their stock as it moves through the supply chain. GTINs such as EAN-13 or UPC-A are necessary for stocking a product with almost all physical and online retailers. The two most widely accepted formats of retail barcodes in the world are the EAN-13 (International Article Number) and UPC-A (Universal Product Code).