A power of attorney is a witnessed legal document between two people that authorizes one person to act for or represent the other, usually in financial matters or when health care decisions are being made. The person granting the power must be fully capable of making decisions in his or her own best interest at the time the document is signed; otherwise the document is invalid.
The person to whom these powers are given is called an agent or attorney-in-fact. The person who is giving decision-making power away is called the principal. Just because the word attorney is used, does not mean that the person to whom the authority (or power of attorney) is given has to be a lawyer.
A power of attorney can be extremely individualized (e.g. “I need help with this specific task from this specific person.”). People may appoint a power of attorney when they are planning to be away from home to ensure that their financial affairs are monitored. Or people may designate a power of attorney to make their medical decisions when they are hospitalized or become ill.