A "folk song" or "folk tune"defined by its source and is still a folk song or tune if performed in a rock style (e.g. Whiskey in the Jar, House of the Rising Sun) but it is not "folk music" if it is performed in a non-participatory context.

Very interesting comments, Mikefule. But if you sing a folk song (say one without a chorus or obvious lines for others to join in), unaccompanied, and no-one but you is singing it, does that make it "non-participatory" , and therefore not folk music? I assume you don't mean that, but can you clarify what you mean by "non-participatory" in this context?