Okay I take the bait albeit under a pseud.
Whilst like anything that attaches itself to the word 'folk' it is almost impossible to define BUT it is possible to make a few generalisations. The real folk are out there singing football chants, bawdy songs, children's rhymes, Beatles and other past popsongs, while the rest of us 'folkies' are enamoured with the pop songs of say 1750-1850 as remembered largely by the real folk of c1890-1920 from their youth. If we really wanted to emulate them we should be doing what my mate Roy Acko largely does in singing the pop songs of his youth. I often make this point by singing in folk clubs 'Gilly Gilly Hosanpeffer whatever' which I remember from my youth.
However some of us simply love the stuff that was popular among the folk c1890-1920, and what's more we're perfectly entitled to, whatever we might call it!