> there isn't a definition in the world which will include Adieu Sweet Lovely Nancy and also include an open-mic cover version of Fire and Rain.

Well, there *is* that pesky definition from the enormous "American Folklore: An Encyclopedia" suggesting that "folksongs" share common ground with "folklore," which is then defined as "verbal arts" or "vernacular culture" or "expressive culture."

Both "Lovely Nancy" and an amateur try at "Fire and Rain" would seem to fit easily into "expressive culture," at the very least. "Vernacular" too.