Pink sheet stocks are stocks that are not listed on a major national exchange but are traded over the counter, according to Investopedia. Pink Sheets is also the name of the publication that lists these bid-ask stock quotation prices.
Companies that trade on Pink Sheets do not have to meet the Securities and Exchange Commission filing and listing requirements, notes Investopedia. These stocks are unregulated, and little information about them is made available to would-be investors. Pink sheet stocks vary widely in quality; some are household names like Nestle or Nintendo, and some are penny stocks of little value. There are about 15,000 stocks that trade on Pink Sheets.