If anyone knows my dad, ask him - he likes folk music he knows his stuff
Now according to wikipedia.....
Charles Seeger (1980) describes three contemporary defining criteria of folk music (Middleton 1990, p.127-8):
A "schema comprising four musical types: 'primitive' or 'tribal'; 'elite' or 'art'; 'folk'; and 'popular'. Usually...folk music is associated with a lower class in societies which are culturally and socially stratified, that is, which have developed an elite, and possibly also a popular, musical culture." Cecil Sharp (1972), A.L. Lloyd ().
"Cultural processes rather than abstract musical types...continuity and oral transmission...seen as characterizing one side of a cultural dichotomy, the other side of which is found not only in the lower layers of feudal, capitalist and some oriental societies but also in 'primitive' societies and in parts of 'popular cultures'." Redfield (1947) and Dundes (1965).
Less prominent, "a rejection of rigid boundaries, preferring a conception, simply of varying practice within one field, that of 'music'."
David Harker (1985) argues that "folk music" is, in Peter van der Merwe's words, "a meaningless term invented by 'bourgeois' commentators".
A Full Definition If Anyone Be Interested.