* Apo, a god of mountains in Inca mythology * Abdullah �calan, nicknamed "Apo", the leader of the Kurdistan Workers Party * Acting Pilot Officer, the lowest commissioned officer rank in the Royal Air Force * Acute Pulmonary Oedema, a medical condition affecting the lungs * African Political Organization, the first major Coloured political organization in South Africa * Alpha Phi Omega (ΑΦΩ), a coeducational service fraternity * Amorphous polycycloolefin, a material used in optical disc substrates * Apochromat, a lens that has greatly reduced chromatic aberration * Apolipoprotein, a lipid-binding protein * Army Post Office, the United States armed forces postal service * Au�erparlamentarische Opposition (Extraparliamentary Opposition), a German part of the New Left movement * Asamblea Popular de los Pueblos de Oaxaca * Audio Processing Object, used in computer programming - esp. Windows Vista sound drivers