Universal Product Code (UPC) is a 12-digit bar code used extensively for retail packaging in United States.
The International Standard Book Number (ISBN) is a unique commercial book identifier barcode. Each ISBN code identifies uniquely a book. ISBN have either 10 or 13 digits. All ISBN assigned after 1 Jan 2007 have 13 digits. Typically, the ISBN is printed on the back cover of the book.
Global Trade Item Number (GTIN) is an identifier for trade items developed by GS1. Such identifiers are used to look up product information in a database (often by entering the number through a bar code scanner pointed at an actual product) which may belong to a retailer, manufacturer, collector, researcher, or other entity. The uniqueness and universality of the identifier is useful in establishing which product in one database corresponds to which product in another database, especially across organizational boundaries.
GTIN-14 (EAN/UCC-14 or ITF-14): this is a 14-digit number used to identify trade items at various packaging levels.