Non-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. In Russian the AA systems are called zenitnye (i.e. "pointing to zenith") systems (guns, missiles etc.). In French, air defence is called DCA (Défense contre les aéronefs, "aéronef" being the generic term for all kind of airborne device (airplane, airship, balloon, missile, rocket, etc.)).
How is the Russian term for air defence abbreviated?
PVO