A broker-dealer is a term used in United States financial services regulations. It is a natural person, a company or other organization that trades securities for its own account or on behalf of its customers.
Although many broker-dealers are "independent" firms solely involved in broker-dealer services, many others are business units or subsidiaries of commercial banks, investment banks or investment companies.
When executing trade orders on behalf of a customer, the institution is said to be acting as a broker. When executing trades for its own account, the institution is said to be acting as a dealer. Securities bought from clients or other firms in the capacity of dealer may be sold to clients or other firms acting again in the capacity of dealer, or they may become a part of the firm's holdings.
Read more about Broker-dealer: Main Points of Activity