It stands for over the counter; a non-physical market place where a widespread assembly of dealers (market makers) and their clients transact away from the premises of organized markets. As opposed to trading on exchanges (bourses), over-the-counter trading takes place through communication means (telephone, computers, etc.) where buyers and sellers negotiate and strike deals. Instruments that trade over the counter are typically not listed (e.g., over-the-counter stock, swap agreements, etc.)

Over-the-counter trading is, therefore, not subject to trading rules or requirements set by a regulatory exchange. Instruments traded over the counter are often more speculative and harbor higher risks than listed ones. Other examples of such instruments include all government and municipal bonds as well as most corporate bonds.