folk music is the music of any peoples of any culture of anywhere. It is different to classical music but its also different to popular music. Folk music is any song sung, tapped, hummed, whistled or played on anything by anyone who isnt a professional musician. Thats not to say professional musicians dont or cant play folk as some of these people could be trained,its worth noting the 'Cultural Assets' policy run for quite some time now in South Korea where skilled musicians considered to be playing national music (and folk is national relative to the context whether pro or anti the location) are taken as cultural assets and required to teach a certain number of people their skills over a period of time. This could be seen as restrictive artistically but questions of aesthetics have no real place in folk music, its only people with comfort that question such things