A Global Trade Item Number (<a href="https://www.gs1.org/standards/id-keys/gtin">GTIN</a>). GTINs identify trade items, including products and services, using numeric identification codes. The <a class="localLink" href="http://schema.org/gtin">gtin</a> property generalizes the earlier <a class="localLink" href="http://schema.org/gtin8">gtin8</a>, <a class="localLink" href="http://schema.org/gtin12">gtin12</a>, <a class="localLink" href="http://schema.org/gtin13">gtin13</a>, and <a class="localLink" href="http://schema.org/gtin14">gtin14</a> properties. The GS1 <a href="https://www.gs1.org/standards/Digital-Link/">digital link specifications</a> express GTINs as URLs. A correct <a class="localLink" href="http://schema.org/gtin">gtin</a> value should be a valid GTIN, which means that it should be an all-numeric string of either 8, 12, 13 or 14 digits, or a "GS1 Digital Link" URL based on such a string. The numeric component should also have a <a href="https://www.gs1.org/services/check-digit-calculator">valid GS1 check digit</a> and meet the other rules for valid GTINs. See also <a href="http://www.gs1.org/barcodes/technical/idkeys/gtin">GS1's GTIN Summary</a> and <a href="https://en.wikipedia.org/wiki/Global_Trade_Item_Number">Wikipedia</a> for more details. Left-padding of the gtin values is not required or encouraged.