The [GTIN-8](http://apps.gs1.org/GDD/glossary/Pages/GTIN-8.aspx) code of the product, or the product to which the offer refers. This code is also known as EAN/UCC-8 or 8-digit EAN. See [GS1 GTIN Summary](http://www.gs1.org/barcodes/technical/idkeys/gtin) for more details.