What are UPCs, EANs, ISBNs and ASINs?

UPC
Universal Product Code (UPC) is (generally) a 12-digit bar code used extensively for retail packaging in United States. (They are sometimes represented as 13 digit codes by adding a leading 0 to make them compatible with EAN’s - see below)

UPC Code
EAN
The European Article Number (EAN) is a barcode standard either 8 or 13 digits - never 12.  Each EAN uniquely identifies the product, manufacturer, and its attributes; typically, the EAN is printed on a product label or packaging as a bar code. We require EAN codes to improve quality of search results and the quality of the catalog as a whole. You can obtain EANs from the manufacturer. If your products do not have manufacturer EANs, and you need to buy EAN codes, you; should go directly to GS1 UK http://www.gs1uk.org

For example, the EAN of  "Colgate Total 75 ml" is 4011200296908
EAN code

ISBN
The International Standard Book Number (ISBN) is a unique commercial book identifier barcode. Each ISBN code identifies uniquely a book. ISBN’s are either 10 digits long or 13 digits long and start with 978 or 979 (i.e. you can convert a 10 digit ISBN to an 13 digit one by adding 978 to the front). All ISBN assigned after 1 Jan 2007 have 13 digits. Typically, the ISBN is printed on the back cover of the book.
 
For example, the ISBN code for J.K.Rowling's "Harry Potter and the Deathly Hallows", Adult Edition, Paperback, UK edition is 978-0747595823, and this code identifies uniquely this book and edition.

ISBN # with EAN Code

ASINs
Amazon Standard Identification Numbers (ASINs) are unique blocks of 10 letters and/or numbers that identify items. You can find the ASIN on the item's product information page at Amazon.com. For books, the ASIN is the same as the ISBN number, but for all other products a new ASIN is created when the item is uploaded to our catalogue. You will find an item's ASIN on the product detail page alongside further details relating to the item, which may include information such as size, number of pages (if it's a book) or number of discs (if it's a CD).

ASINs can be used to search for items in our catalogue. If you know the ASIN or ISBN of the item you are looking for, simply type it into the search box (which can be found near the top of most pages), hit the "Go" button and, if the item is listed in our catalogue, it will appear in your search results.

For example, the ASIN for Hasbro's "Monopoly" game is B00005N5PF.