Strictly speaking, an "attorney" is one who acts on behalf of another person in some capacity. An "attorney-in-fact" is akin to an agent who acts on behalf of another person, typically with respect to business, property, or personal matters. Such an agent does not have to be licensed to practice law and may not need to have any license at all.
By contrast an attorney-at-law, or lawyer, is a person trained and licensed by a relevant jurisdiction to practice law by representing clients in legal matters and giving legal advice. In the United States, the term attorney, standing alone, generally refers to this meaning rather than to "attorney-in-fact".
The term "attorney-in-fact" is mostly seen in the context of someone representing another person's interest in business negotiations or regarding signature pages on documents where the person signing is doing so on the basis of a power of attorney. The term power of attorney generally relates to an attorney-in-fact, not an attorney-at-law. Alternative titles for "power of attorney" type documents in non-U.S. jurisdictions include the French "Pouvoir", the German "Vollmacht" and the Portuguese "Procuracao".
