A listed security is a stock, bond, options contract, or similar product that is traded on an organized exchange.
Being listed has advantages, including being part of an orderly, regulated, and widely reported trading process that helps insure fairness and liquidity.
To be listed, the company issuing the security must meet the requirements of the exchange where it wishes to be traded. For example, to list a stock, the company typically must have a minimum market capitalization, a minimum number of existing shares, and a minimum per share price.