A short, or a short position, is created when a trader sells a security first with the intention of repurchasing it or covering it later at a lower price. A trader may decide to short a security when she believes that the price of that security is likely to decrease in the near future. There are two types of short positions: naked and covered.
A naked short is when a trader sells a security without having possession of it. However, that practice is illegal in the U.S. for equities. A covered short is when a trader borrows the shares from a stock loan department; in return, the trader pays a borrow-rate during the time the short position is in place.
