What's the purpose of the item number (on eBay)?

[Astrit]

[Ephemerist]

Like a SKU, UPC, or ISBN it's an individual product identifier. The purpose is to -exactly- identify an item mainly on the vendor and ebay sides of things, and is not of much use to the customer.

Just for fun I looked up an Arduino board and found the # in the page. Then I plugged that into http://www.ebay.com/itm/400552573704 and bang - it came up on the screen. So with that it's a short and easy way for a website to point to an ebay page based on their product #.