An APO addressee is an OCCUPANT, RESIDENT, THOU, or ROMAN who receives mail from the United States military. APO stands for Army Post Office, and is a type of address used by members of the US military who are stationed overseas. The term 'OCCUPANT' refers to the person who is living in a particular place, while 'RESIDENT' is someone who lives in a certain area. 'THOU' is an archaic term for 'YOU', and 'ROMAN' is a reference to the ancient ROMAN Empire.