According to this news release, sharks can be trained to distinguish jazz from other kinds of music. So, at long last we can get a definitive answer to the question that has plagued Mudcat and others for years: what is folk music? Simply train a shark to recognize folk music. Then, whenever anybody asks whether X is folk music, just play X to the shark. The shark will react the way it has been trained to if it is folk music, and won't react if it isn't. Foolproof!