Oh God, the what-is-folk virus has crept into yet another thread... Actually I quite enjoy the effects, so loong as we realize there is never going to be a answer.

"What is folk?" is a bit like "what is money?" - is a foreign coin, or a coin or note that is no longer legal tender really money? For some purposes, like collecting or tossing a coin it is, for other purposes, like spending, it's not. And then some foreign currency which isn't legal tender is perfectly acceptable in m many shops. And where does barter and plastic crdit and debit cards and IOUs come?

The popint is the things that human beings use to deal with each other can't in practice be tied themselves down to neat categories. A bit of paper or metal will count as money here and not there, and now and not then. And the same goes for a song counting as folk.