Broker

A broker is a party that mediates between a buyer and a seller.

A brokerage or a brokerage firm is a business that acts as a broker.

A sales person working for a securities or commodity brokerage firm is generally also called a "broker," although this is technically incorrect. This sales person is infact an exchange member who actually executes the purchase or sale order, on the exchange, as a service to the client of the firm for which that salesman works.