A share of “stock” represents partial ownership in a business. If you are the sole owner of a business that is organized as a corporation, then you own 100% of the stock of that business. If you are the sole owner of a business that is organized as a limited liability company (“LLC”), then you own 100% of the membership interests of that business. When one speaks about the price of a publicly-traded company’s stock going up or down, they usually are referring to the common stock of the corporation. However, some corporations have multiple “classes” of common stock, with each class having different rights. For more information, see Investing Basics For Beginners Installment #1: What is Stock? And Should You Buy Some?