Hmmm. Hard to say, because al song or dance tunes were written by someone originally.
I'd define it as a tradition reflecting a particular society and time, of possibly and usually unknown authorship, and intended for popular performance and entertainment.
I would classify the original blues and styles like Zydeko as a form of folk, alongside Irish and Scots dance music and the English morris tradition, along with equivalents from around the world,. Yet I exclude modern Country & Western and the likes of Joan Baez, or Ewan McColl and his wide Peggy Seeger. These exclusions are not "inferior" or superior", but are the style of rather than being, "traditional" - if you define that as long-standing provenance and unknown origin. To me, they exaggerate the genre to self-parody and I find some of their products rather embarrassing.
On the other hand, what of a lot of so-called (by them as don't know) "classical" music? A lot of that took contemporary folk and dance music for inspiration, even if the arrangements go far from the original.
It's very hard to describe such things objectively thanks mainly to personal taste. One of the best and most popular modern folk-tradition songs is one of my favourites, and even thinking of it chokes me. It is Where The Time Goes, by the English folk-rock band Fairport Convention - not least thanks to to the singing style of Sandy Denny, who was its composer, I think before she actually joined the band. Now, is that folk, or in folk style? I don't know, but I do know covers I have heard by Lionel Ritchie and some American opera-singer you'd expect to sing it rather better than him or indeed Sandy herself, make a right hash of it.
A point sometimes made by folk musicians is that real folk music is very flexible. It does not really matter if you perform on guitars and drums what was originally scored for sackbut and serpent, as long as you respect it.
I agree. It is for entertainment, capable of performance and enjoyment down the ages by people who may not have a formal musical education but who appreciate simple song and dance music played and sung well. Considerable differences from both formal orchestral music demanding great skill to perform and some concentration by the listener to appreciate fully, or modern pop that is essentially a paen to comformist inability.
