After some digging:

'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).

Pretty much my own definition that I came up with all on my own (more or less)