Anti-aircraft warfare or counter-air defence is defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action." They include ground-and air-based weapon systems, associated sensor systems, command and control arrangements and passive measures (e.g. barrage balloons). It may be used to protect naval, ground, and air forces in any location. However, for most countries the main effort has tended to be 'homeland defence'. NATO refers to airborne air defence as counter-air and naval air defence as anti-aircraft warfare. Missile defence is an extension of air defence as are initiatives to adapt air defence to the task of intercepting any projectile in flight. 

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.)). QUESTIONS:

Q1:
1. What's the definition of anti-aircraft or counter-air defence?
2. What do the terms anti-aircraft or counter-air defence mean?
3. What is meant by anti-aircraft or counter-air defence?
Q2:
1. Who defined anti-aircraft or counter-air defence?
2. Who gave a definition of anti-aircraft or counter-air defence?
3. Who stated what anti-aircraft or counter-air defence mean?
Q3:
1. How many elements of anti-aircraft or counter-air defence are there?
2. How many things are included in anti-aircraft or counter-air defence?
3. What is the number of aspects of anti-aircraft or counter-air defence?
Q4:
1. What's one element of anti-aircraft or counter-air defence?
2. What is an aspect of anti-aircraft or counter-air defence?
3. What's one thing that is included in anti-aircraft or counter-air defence?
Q5:
1. What do most countries focus their efforts on?
2. What is the most prominent effort in the majority of countries?
3. Which effort are most countries concerned with?
Q6:
1. What do they call anti-aircraft or counter-air defence in France?
2. What is the French term for anti-aircraft or counter-air defence?
3. What do the French use for anti-aircraft or counter-air defence?
Q7:
1. What do they call anti-aircraft or counter-air defence in Germany?
2. What German force does anti-aircraft or counter-air defence?
3. What do the Germans use for anti-aircraft or counter-air defence?
Q8:
1. What does Flak do?
2. What is the task of Flak?
3. What task does the German Flak force have?
Q9:
1. What do they call anti-aircraft or counter-air defence in Russia?
2. What Russian force does anti-aircraft or counter-air defence?
3. What do the Russians use for anti-aircraft or counter-air defence?
Q10:
1. How many examples of non-English terms for air defense are given?
2. How many terms for air defense not in English appear?
3. What is the number of terms for air defense that appear in a non-English language?
