What is the meaning of missing?

(DoD) A casualty status for which the United States Code provides statutory guidance concerning missing members of the Military Services. Excluded are personnel who are in an absent without leave, deserter, or dropped-from-rolls status. A person declared missing is categorized as follows. a. beleaguered--The casualty is a member of an organized element that has been surrounded by a hostile force to prevent escape of its members. b. captured--The casualty has been seized as the result of action of an unfriendly military or paramilitary force in a foreign country. c. detained--The casualty is prevented from proceeding or is restrained in custody for alleged violation of international law or other reason claimed by the government or group under which the person is being held. d. interned--The casualty is definitely known to have been taken into custody of a nonbelligerent foreign power as the result of and for reasons arising out of any armed conflict in which the Armed Forces of the United States are engaged. e. missing--The casualty is not present at his or her duty location due to apparent involuntary reasons and whose location is unknown. f. missing in action--The casualty is a hostile casualty, other than the victim of a terrorist activity, who is not present at his or her duty location due to apparent involuntary reasons and whose location is unknown. Also called MIA. See also casualty category; casualty status.