SKU = Stock Keeping Unit
It's a standard term for one type of stock.
Example:
SKU# 3358 7231 Men's T-shirt Addidas Black wStripe XL
SKU# 3358 7241 Men's T-shirt Addidas Black wStripe XXL
SKU# 3358 6311 Men's T-shirt Addidas Gray Plain M
An individual code can usually identify the category, manufacturer, specific product and then the variation on that product. In the case of the first two, the products are identical apart from the size and so only the last two numbers change. In the third example, the category and manufacturer are the same but the product is different and so we see a greater change.
Each manufucturer has it's own SKU system which can also contain letters and dashes as it needs - point being that each number corresponds to a specific line of product. Retailers can then use their own SKU systems as well. Almost all products also conform the the Universal Product Coding system (UPC) which is the 10-12 digit barcode you see on pretty much anything that is boxed, bagged or tinned.
When a manufacturer says they are introducing a new SKU - there are basically saying they are introducing a new line of product.
I.E. - ithe existing 60 GB playstation sku for Europe is CECH C04 where CE is the PS3 class, CH refers to a playstation 3 itself, C refers to a 60 GB machine, 0 refers to 1st run and 4 refers to European region (this is subject to confirmation)
Therefore - if Sony decides to introduce a new SKU which would be a 60 GB with a 65nm processor and no card reader to achieve a better price point, the code might be: CECHC14 where everything is the same except that this would be the second run of a 60gb machine.
Alternatively - Sony introduces a new controller (no previous design) for the PS3 for Australia (region 2) - the code might be CEQRM02 where CE refers to Playstation class, QR refers to the new controller type, M might refer to the colour, 0 refers to 1st run and 2 identifies Australia as the region for sale.
Confused? Good.
