What is the meaning of Unlisted security?

Unlisted security is a security, such as a stock, is unlisted when it cannot meet the listing requirements of any of the organized exchanges or markets. The stock can be traded over the counter (OTC), however, and may be included in the pink sheets published by the National Quotation Bureau or on the OTC Bulletin Board. Since in order to be listed, a company has to have a certain market capitalization, a minimum number of outstanding shares, or comparable indication of staying power, many unlisted stocks are those of small companies that may someday meet those requirements and be listed. In most cases, unlisted stocks are thinly traded because they do not get much attention from the media or financial analysts, and are judged to be too risky for many investors.