Originally Posted by tiger

Sorry but wrong.

Short selling is selling shares you don't own. If you owned them it would just be regular sale.

Naked shorting is more complicated.

"Naked short selling, or naked shorting, is the practice of selling a stock short without first borrowing the shares or ensuring that the shares can be borrowed as is done in a conventional short sale. When the seller does not then obtain the shares within the required time frame, the result is known as a "fail to deliver.""

You can read more here: http://en.wikipedia.org/wiki/Naked_short_selling