A document that gives another person the power and legal authorization to act on your behalf. The maker of the document is the principal and the agent who is designated is the attorney-in-fact. A durable power of attorney provides authorization in the event the maker becomes incapacitated, for example, comatose and near death. See durable power of attorney for finances; durable power of attorney for healthcare. An instrument authorizing a person to act as the agent or attorney of the person granting it See LETTER OF ATTORNEY.