Investors should not confuse the short sale of a home and the short sale of a stock. Buying a stock means you are purchasing interest in a company and is bought by increments of shares. For example, one share of IBM could be $87 per share. You can sell the stock anytime that you want. If you are shorting a stock you are essentially buying a contract that is betting that the stock price will go down within a specific time period. You make money based on how much the stock goes down in value and lose money if the stock increases in price.