Over-The-Counter Market

What Does Over-The-Counter Market Mean?
A decentralized market of securities not listed on an exchange where market participants trade over the telephone, facsimile or electronic network instead of a physical trading floor. There is no central exchange or meeting place for this market.

Also referred to as the "OTC market".

Investopedia explains Over-The-Counter Market
In the OTC market, trading occurs via a network of middlemen, called dealers, who carry inventories of securities to facilitate the buy and sell orders of investors, rather than providing the order matchmaking service seen in specialist exchanges such as the NYSE.