I don't understand and tend to disagree with the definition of falsetto as "an artificial extension of the tenor range".

How, "artificial"? What, is there surgery? Medications? Do they use special mechanical appliances? Or is it done in the electronics after recording?

Of course not. It's a vocal technique, using what the singer has naturally. Just because not everyone is able to do it or doesn't bother to learn it doesn't make it artificial. It would be just as meaningful to call ordinary singing artificial, or to call hand-clapping artificial. Yes, of course it's man-made, but so are those things.

Dave Oesterreich