A company is referred to as a public company if its common stock is listed on a public exchange. Examples of public stock exchanges are: Nasdaq, the New York Stock Exchange, and the American Stock Exchange. Shareholders of public companies can easily sell their shares of common stock on these exchanges.

If a company is not a public company, then it is a private company, which simply means that all its shares of common stock are held privately. A private company doesn't need to share any information about its finances with the public, but a public company does need to publicly disclose much of its financial information. Shareholders of private companies often have difficulty selling their shares of common stock.