What is the name given to the person who is authorized to act on behalf of another person?

The term used to refer to a person who is authorized to act on behalf of another is "agent." In the context of real estate and other transactions, an agent has the legal authority to represent and make decisions for someone else, known as the principal. This relationship is often formalized through a contract or agreement which outlines the scope of the agent's authority.

An agent is responsible for acting in the best interest of the principal, which involves fiduciary duties such as loyalty, disclosure, and accounting. This role is crucial in various scenarios, such as real estate transactions where agents represent buyers or sellers to negotiate and facilitate deals.

In contrast, other terms mentioned in the question refer to different relationships or roles within a transaction. A broker typically manages agents and handles business operations within real estate, while a principal is the individual or party who grants authority to the agent. A trustee is someone appointed to manage a trust, which involves overseeing property or assets on behalf of beneficiaries, but does not necessarily imply the same agent-principal relationship as described in the question. Thus, the clarity of the agent's role in representing another person makes this option the correct answer.