PS - If the ITCM usage of Popular was synonomous with Folk (as you appear to be suggesting) then why do they use Folk as well? Indeed, I have seen enthnomusicological dissertations on everything from Barber Shop Quartets of Hartlepool, the Village Gamelans of Sunda, the Heavy Metal Bands of Birmingham to the Hip-Hop Crews of Clapham, all of which fall under the heading of Popular in precisely the same way Child used the term. Folk is a later construct which became a genre covering an ever widening multitude of idioms and possibilities with the emphasis on self-conscious revival, conceit, puritanism, conservatism, fundamentalism, nostalgia & other such wonky contrivances. I see no harm in that myself of course; folk is my country in which I am quite happily, and wonkily, astray.