The religious war over the definition of "folk" music and "folk" songs resumes every few months in this forum, and it's usually entertaining.

Peter Schickele once did an episode of "Schickele Mix" entitled "Folk music--schmolk music" in which he disputed the question with himself, he, and him.

For those who would rather avoid the quarrel, perhaps a good technique is to distinguish "folk" as a musical idiom (in which case it would be most related to "old-timey" music, but have elements in common with other musical idioms) from "folk" music as a description of how music is used. My favorite definition of the latter kind is: folk music is music that people use while they are doing something else. A shape-note hymn sung as a concert piece to a passive audience is not folk music. The same hymn sung in worship is folk music. If you play a Mozart symphony on your stereo and simply bathe in the music, it is not folk music. If you vacuum your floor while it plays, it is folk music.