作多（go long）和放空（go short），以及空頭（short-seller）

保羅．克魯曼（Paul Krugman）寫的《面對失靈的年代：克魯曼談金融海嘯》（The Return of Depression Economics and the Crisis of 2008）一書如此解釋：

Basically, to go long in something is to put yourself in a position to gain if its price rises—which is what the ordinary investor does when buying stock, real estate, or anything else. To go short in something is to put yourself in a position to gain if its price falls. To sell a stock short, one borrows the stock from its owner with a promise to return it later—then one sells it. This means that the stock must be repurchased before the due date; the short-seller is betting that its price will have fallen by then. Meanwhile, the short-seller has acquired extra cash, which can be invested in something else—that is, he takes a long position in some other asset.