Is willingness to pay part of the definition of a "market"? (Honest question; I didn't go to business school.) I don't doubt there are "tens of millions of folk

Is willingness to pay part of the definition of a "market"? (Honest question; I didn't go to business school.) I don't doubt there are "tens of millions of folks who would use this over an iPad" if it were free -- I'm one of those people -- but to buy this in addition to, or instead of, an iPad? No way.