Final answer:
The term for a person who has the authority under a power of attorney is attorney-in-fact.
Step-by-step explanation:
The term for a person who has the authority under a power of attorney is attorney-in-fact. An attorney-in-fact is an individual appointed by someone, known as the principal, to act as their agent and make decisions on their behalf. The authority granted to the attorney-in-fact can be broad or limited depending on the terms of the power of attorney document.