'Folk music is the product of a musical tradition that has been evolved through the process of oral transmission. The factors that shape the traditions are: (i) continuity which links the present with the past; (ii) variation which springs from the creative impulse of the individual or the group; and (iii) selection by the community, which determines the form or forms in which the music survives. […] The term does not cover composed popular music that has been taken over ready-made by a community and remains unchanged, for it is the re-fashioning and re-creation of the music by the community that gives it its folk-character (Journal of the International Folk Music Council, VII, 1955, p. 23).

I've used a version of this definition when talking about Irish music and song to groups of international students - and then set them a set of questions to think about, based on it. Probably the most interesting is to ask "Yes, but - what does "community" mean now?"

Regards

p.s. I'm not suggesting, of course, that the definition and its implications be laid out like a row of dead fish on a slab - just that it and they provide a framework for choosing examples, for provoking discussion and for providing insight.