Short Selling Short selling is a trading strategy

Short Selling
Short selling is a trading strategy where an investor, believing that a security is over-valued, borrows (from a broker-dealer or institutional investor) and sells a security and then repurchases and returns (to the broker-dealer or institutional investor) the security at a lower price. The difference between the sale price and the purchase price is the investor's profit.
Short selling is a valid trading strategy; however, there are two important points that investors must remember:
Short selling carries with it unlimited risk because the purchase price of a security can rise to any price point. Conversely, long investors (buyers) may only lose the amount invested — if, for example, the security price drops to zero.
Short sellers are subject to price manipulation schemes — or short squeezes. In a short squeeze, traders believing that there are a lot of short sellers begin buying shares to force the price and the short sellers losses higher. These traders hope that the short sellers will be forced to buy pushing the price even higher at which point they can sell their shares at a profit. Short squeezes are easier to execute in illiquid securities.