Anyone care to comment on how this works in other langauges and cultures? I think what we've got here is a uniquely Anglo-American development. As I understand it:

Turkish: "halk muzigi" means folk music in a pretty narrow sense definitionally, but with a very wide audience. Doesn't matter who's playing it or on what instruments, but melody is nearly always either improvised or anonymous trad and the text will be from anonymous tradition or bardic lineage most of the time. Singer-songwriter is "özgün" and not all that popular any more. Folk tunes and lyrics are often adopted by rock and pop musicians, but they don't think of themselves as "folk-rock" or "pop-folk" for doing so, it's just a natural thing for them to use.

German: "volkslied" has a narrow denotation, pretty much the 1954 one but with extra-careful footnotes to sidestep the way the Nazis tried to take it over. Singer-songwriter is just "lied" with no linguistic category distinction being made between Schubert and Wolf Biermann.

Italian: "canti populari" means folk in a very narrow traditional sense, so narrow that it doesn't actually have much of an audience.

Hungarian: the word "nép" means "folk" in a national as well as sociological sense. There doesn't seem to be a single word that covers the traditional music of all the ethnic groups in the areas where ethnic Hungarians live, but there is so little musical interchange between them it doesn't actually matter all that much. They had a particular problem in trying to separate out the bourgeois wannabe-folk of the 19th century, but for better or worse that stuff has largely gone the way of Moore's Irish Melodies by now - dead genres don't need labels.

French: their terminology seems a bit of a mess to me and I don't understand it, but it's a different kind of mess from English.