Wikipedia describes real estate agents and buyer agents in the following way. However, this definition puts agents, salespersons, and brokers in one big category. Read further about their different roles and capabilities in other areas on this site.
“A real estate broker or real estate salesperson (often called a real estate agent) is a person who acts as an intermediary between sellers and buyers of real estate/real property and attempts to match up sellers who wish to sell and buyers who wish to buy.
In the United States, the relationship was originally established by reference to the English common law of agency, with the broker having a fiduciary relationship with his or her clients. A real estate broker typically receives a payment called a commission for successfully matching a seller’s real estate with a buyer such that a sale can be made. This commission can be divided up with other participating real estate brokers or agents when applicable.
An estate agent, which is a term used in the United Kingdom, is a person or business entity whose business is to market real estate on behalf of clients. There are significant differences between the actions, powers, obligations, and liabilities of brokers and estate agents in each country. Other countries take markedly different approaches to the marketing and selling of real property.
In the United States, however, real estate brokers and their salespersons who assist owners in marketing, selling, or leasing properties are commonly called “listing brokers” and “listing agents.”  Listing brokers and agents seek to market and sell or lease property for the highest available price under the best available terms.
Other brokers and agents may focus on representing buyers or tenants. However, licensing as a broker or salesperson authorizes the licensee to represent parties on either side of a transaction. The choice of which side to represent is a business decision for the licensee.
In the U.S., real estate brokers and salespersons are licensed by each state, not by the federal government. Each state has its own laws defining the types of relationships that can exist between clients and real estate licensees, and the duties of real estate licensees to clients and members of the public. These rules differ substantially from state to state, for example, on subjects that include required documentation, agency relationships, inspections, disclosures, continuing education, and other subjects.”