What it is:
A short sale is a three-step trading strategy that seeks to capitalize on an anticipated decline in the price of a security.
How it works/Example:
First, arrangements are made to borrow shares of the security, typically from a broker. Next, the investor will sell the shares immediately in the open market with the intention of buying them back at some point in the future. Finally, to complete the cycle, at a later date he/she will repurchase the shares (hopefully at a lower price) and will return them to the lender. In the end, the investor will pocket the difference if the share price falls, but will of course incur a loss if it rises.
Let's look at an example:
Mr. Johnson firmly believes that ABC Corp. stock is due to fall, so he calls his broker to sell short 100 shares of the company.
In this example, we will assume that Mr. Johnson places the trade, which is immediately executed, to sell short 100 shares of ABC Corp. at $25.00 per share. He will receive a cash inflow of $2,500 from this transaction.
Now let's assume that two weeks later, the price has indeed dropped, and that Mr. Johnson is able to buy back the shares (known as covering a short position) for $20.00 per share. In this transaction, he'll have to spend $2,000 to repurchase the shares. His profit on the trade will be $500 ($2,500 initial cash inflow minus an eventual $2,000 cash outflow). The other way to look at it is that he will have earned $5 per share on the trade, giving him a gain of $500 ($5 gain multiplied by 100 shares). Using this same calculation, we can see that if the shares had risen to $27.50 during his holding period, then he would have been responsible for a $250 loss (100 shares * $2.50/share).
Why it matters:
Essentially, a short seller is still trying to do the same thing a regular investor is -- buy low and sell high. However, the short seller is trying to accomplish this in reverse order. In other words, he/she is trying to first sell high and then buy low. The short sales strategy, which is the opposite of entering a long position, is a risky one for a number of reasons. These include the potential for a margin call, as well as theoretically unlimited losses should the underlying stock rise instead of fall. A short seller is not entitled to keep any dividends distributed while he/she has shorted a stock.
When a large number of investors decide to short a particular stock, their collective actions can have a dramatic impact on the company's share price. An investor can quickly determine the percentage of a company's outstanding shares that are currently being sold short by checking the stock's "short interest." For example, a 10% short interest means that one of every ten outstanding shares is held short.
Often, market analysts or financial journalists will attribute a rise in a given stock, or occasionally even the broader markets, to short covering. Eventually, all short sellers must close out their trades by repurchasing the underlying shares that they initially sold. If many of them begin to do this simultaneously, then the rush of buying orders can temporarily boost stock prices. This often occurs after the market has fallen steeply (as short sellers attempt to lock in gains) or while it is rising sharply (as short sellers try to prevent further losses).
Occasionally, a sharp rise in a particular stock can trigger a large number of short sellers to cover their positions all at once. This short covering can push the share price even higher, causing even more short sellers to cover their positions and cut their losses. In these cases, the stock is said to be caught in a short squeeze. Volatile stocks with large short interest are particularly susceptible to this phenomenon, and prospective short sellers should be wary of it.
Though they are a small minority, a few investors actually own shares in the company they intend to short. This alternate strategy -- known as shorting against the box -- is typically used when an investor expects the price to fall, but does not yet want to close out his/her position by selling his/her current long positions.