Was it Dr Johnson or the first editor of the OED that defined the English language along these lines:

It has a large circumference has a very definite and well recognised centre, but as you approach the periphery it becomes nebulous to the point that you cannot see what is and isn't inside.

Not a definition of Folk but a good description of the definition.

If the concept is sufficiently large to sustain sub-divisions can we accept the concept of trad Folk and "modern" Folk? along with the myriad: Song, music, custom, story, joke, (etc) on a second dimension. I am sure we could introduce a third axis (at least) say - timescale.

Given the way it is discussed here it is obviously multi-dimensonal. More rounded if you like. Whatever - Folk doesn't have blinkers. folk do.