A broker is: 

1.     An individual or firm that charges a fee or commission for executing buy and sell orders submitted by an investor.

2.     The role of a firm when it acts as an agent for a customer and charges the customer a commission for its services. 

3.     A licensed real estate professional who typically represents the seller of a property. A broker's duties may include: determining market values, advertising properties for sale, showing properties to prospective buyers, and advising clients with regard to offers and related matters.