Heard on the radio this morning, "a folk song is a song which does not have a definitive version". It gets passed around, fooled around with, changed, arranged every which a-way. Pretty broad definition, eh?
Perhaps some of us would like to talk about traditional ballads and traditonal ballad singing. That narrows the style definition, doesn't it? When you add, for example, piano background to what was intitially a simple traditional ballad and the text plays less of a role than what is being done to embellish the tune, I question whether the presentation remains "traditional ballad".