GTIN stands for Global Trade Identification Number. This refers to any type of barcode that is used in the Global Retail System. So it can refer to a variety of different barcodes. I have detailed the most common of these below.
GTIN-12 – this refers to UPC-A or UPC-12 barcodes. These are used on products and are used primarily in the USA and Canada. These can be purchased here.
GTIN-13 – This refers to an EAN-13 barcode. These are the most common type of barcode used for retail and is common in all countries. These can be purchased here.
Please see the differences between EAN-13 and UPC-A barcodes here.
GTIN-14 – This refers to ITF-14 or TUN Carton Codes. These are used for cartons of 6 or 12 (or any number) of your product and is used purely for stock tracking by the company. It is based on a UPC-A or EAN-13 barcode so the ITF-14 on a carton corresponds to the EAN-13 on the product inside the box.