It is when shares of a stock are sold/shorted that don't really exist... Basically counterfeiting the stock. The effect of more shares on the market than actually exist equates to a float much larger than the company actually released. CHNW has indicated that as many as 1 BILLION of these counterfeit shares exist in their stock alone. Hence the cusip & name change in an effort to force the shorts to cover.
For the details of how it actually happens, there is a verrrrry informative presentation by the CEO of Overstock.com (kind of the poster boy for naked shorting now) here: http://www.businessjive.com/nss/darkside.html
It takes about an hour to get through, but it is very eye opening and done in a manner that anyone can follow.
Mind blowing to think that it is as rampant as many claim it to be, but really not all that hard of a picture to paint... Greed and money!!