GTIN stands for Global Trade Item Number.
This is the number used to identify a product. It is often incorrectly called a "barcode" or "barcode number" but these terms are wrong and potentially confusing. A GTIN may be encoded in any one of many barcodes so should be thought of separately.
For example both a GTIN-13 (GTIN with thirteen digits) or a GTIN-14 (GTIN with fourteen digits) could be encoded in ITF-14, GS1-128, GS1 DataBar Omnidirectional, GS1 DataBar Expanded, GS1 Data Matrix, or GS1 QR Code barcodes. So in rare circumstances could GTIN-8. GTIN-13 however is usually encoded in EAN-13 only and GTIN-8 is generally found only in EAN-8 or UPC-E bar codes.
These examples show how the use of incorrect terminology risks serious confusion and errors.