qnli question: How is the Russian term for air defence abbreviated? sentence: English terms for air defence include the German Flak (Fliegerabwehrkanone, "aircraft defence cannon", also cited as Flugabwehrkanone), whence English flak, and the Russian term Protivovozdushnaya oborona (Cyrillic: Противовозду́шная оборо́на), a literal translation of "anti-air defence", abbreviated as PVO.