Ever wonder what folks mean when they refer to "private" and "public" companies? If so, read on.

A private company is one that's privately owned -- usually by one or a few people. Its owners don't have to reveal much about their business, and most of us investors can't invest in it. A public company, on the other hand, is one that has sold a portion of itself to the public via an initial public offering (IPO) of some shares of its stock. Therefore, it probably has hundreds or thousands of co-owners. If it's an American company trading on American stock exchanges, it's required, among other things, to file quarterly earnings reports with the Securities and Exchange Commission (SEC). These are also made available to shareholders and the public. A public company can't keep mum about how much it made in sales last year. It must report information like that -- its revenues, cost of sales, tax expenses, administration costs, debt load, cash level, and so on.

Here are a bunch of major companies that are private, in descending order of annual revenues, per Forbes magazine in 2005: Cargill, Koch Industries, Mars, Pricewaterhousecoopers, Publix Super Markets, Bechtel, Ernst & Young, Cox Enterprises, Toys "R" Us, Fidelity Investments, Swift & Co., SC Johnson & Co., Boise Cascade, Giant Eagle, Gulf Oil, Hallmark Cards, Levi Strauss, Hearst, Neiman Marcus, Bloomberg, Colonial Group, Kohler, Wegman's Food Market, 84 Lumber, Mervyn's, Booz Allen Hamilton, McKinsey, Perdue Farms, JR Simplot, Wawa, Cumberland Farms, Edward Jones, Gilbane, and E&J Gallo Winery (this list isn't comprehensive in any way.) Some international biggies include IKEA, Seiko, Bertelsmann, Virgin Group, and LEGO. Some of these firms offer shares to employees, but individual investors are out of luck.

Just because an old, established firm is private doesn't mean it'll always be private -- United Parcel Service (NYSE:UPS) and Goldman Sachs (NYSE:GS) were both established as private companies, but both went public a few years ago. Levi Strauss, once private, went public only to go private again.

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