The European Article Number (EAN) is a universal identifier for products, commonly printed in form of barcodes on them. The numbers represented by those codes can either be 8 or 13 digits long, with the 13-digit-version being most common. EANs form a superset of the North American Universal Product Code (UPC) as every UPC can be made an EAN by adding a leading zero to it. Additionally every EAN is also a Japanese Article Number (JAN).
The identifiers were formerly assigned by EAN International which merged with Uniform Code Council (UCC, the guys behind the UPCs) and Electronic Commerce Council of Canada (ECCC) to become GS1.
A generalised term for EANs, UPCs and JANs is Global Trade Item Number (GTIN). MusicBrainz now allows the storage of GTINs with release events, in the 'barcode' field of each release event. Before this was possible, this information was commonly stored in release annotations, using the unofficial ReleaseAnnotationStyle.