If the term "folk" has any meaning at all, I would think that the wonderful music of Django is NOT folk.

It IS loose and improvisational, as someone noted above as justication FOR the "folk" label, but is that really a valid criterion? If so, jazz of all kinds ~ including the most abstract post-modern forms that folk-purist types seem to absolutely abhor ~ would fit under the definition of "folk."

My own very ideosyncratic definition of "folk music" is "music that is familiar to the just-plain folks of a given community." To me, then, favorite pop tunes (e.g., "oldies") qualify as "folk music" of the worldwide musical culture that shares access to and interest in the internet. Whatever you can sing along with, in other words.

Sing-along-ability is NOT a characteristic of Django's brilliant instrumental work, no moreso than that of, say, John Coltrane or Philip Glass. To me, music intended for performance rather than primarily for participation is not really "folk."

Now, someone else's definition of "folk" might well encompass performance art, as long as the music being performed duplicates some old-time musical canon that once belonged to some community of villagers or fishermen, etc., who were able to sing and play that music together. To me, that kind of thing may evoke folk music, or may once have been folk music, but now it ain't; it's art music.