Short Selling
The normal process of "going long" involves buying first and selling last, hopefully at a higher price. Short selling is the same concept of buying low and selling high, but in the reverse order. You borrow some stock from your brokerage and immediately sell it on the market. After the stock drops in price you must buy some shares from the market and return them to your brokerage. It sounds complicated at first, but it is really almost as easy as "going long."