here si some info about short...on shares...
The Basics
When an investor goes long on an investment, it means she has bought a stock believing its price will rise in the future. Conversely, when an investor goes short, he is anticipating a decrease in share price.
Short selling is the selling of a stock that the seller doesn't own. More specifically, a short sale is the sale of a security that isn't owned by the seller, but that is promised to be delivered. That may sound confusing, but it's actually a simple concept.
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