There sure are a lot of acronyms on Amazon, and a lot of unique identifiers as well.  Hopefully this will clarify for you!

ASIN

Every item that is in the amazon product catalog is assigned a unique ASIN. If you create a new listing, it will get a new ASIN.  If you’re a wholesaler listing on an existing catalog item, you’re listing on an existing ASIN.  In short, each item that comes up in search is a unique product detail page, and it has an ASIN.

Variations of the same product still have a unique ASIN for each variation.  For example, if you’re creating 2 variations for baseball caps, by color, Red and Blue, you’d have 3 ASIN’s: 1 for Red, 1 for Blue, and 1 for the parent item that binds the two together, but is never seen in search.

To sell an ASIN, you create an “offer” so that your offer can be listed on that ASIN’s product detail page.  On popular wholesale items, there can be a hundred different offers per ASIN.

SKU

SKU is short for Stock Keeping Unit – it’s what you call the product in your system.  You can use whatever naming convention you want here.  A lot of people use a pattern like Brand-Model-FulfillmentMethod to name their products. Always ensure you make SKU’s mean something so that when you see it in a list, you’ll know what product/variation it’s talking about. Every time you create a new offer for an ASIN, you’ll be asked to provide a unique SKU.

FNSKU

The FNSKU is the alphanumeric number that is used to generate the barcode that you put on your product when you send inventory to the FBA warehouse.  Each “Fulfilled by Amazon” SKU you add to Amazon will have it’s on FNSKU Barcode. You’re not required to use FNSKU’s to list on Amazon.  You can also use the manufacturer barcode (UPC) that is printed on the product package.

UPC

A UPC is a Universal Product Code.  Every item you buy in the supermarket has one, it’s what they scan at checkout.  UPC’s are purchased, from GS1, who holds the rights to distribute them, and anyone in the world who looks up your UPC on any system can find out what the product is.  Each product on Amazon, unless you’ve been given an exemption, requires a UPC.

EAN

EAN is the European version of the UPC barcode.