An officer of the United States is a functionary of the executive or judicial branches of the federal government of the United States to whom is delegated some part of the country's sovereign power. The term officer of the United States is not a title, but a term of classification for a certain type of official.
Under the Appointments Clause of the Constitution, the principal officers of the U.S., such as federal judges, ambassadors, and "public Ministers" (Cabinet members) are appointed by the president with the advice and consent of the Senate, but Congress may vest the appointment of inferior officers to the president, courts, or federal department heads. Civilian officers of the U.S. are entitled to preface their names with the honorific style "the Honorable" for life, but this rarely occurs. Officers of the U.S. should not be confused with employees of the U.S.; the latter are more numerous and lack the special legal authority of the former.