Sleepy Rosie: a couple of the "observable characteristics" of folk music (using the term as a lot of longterm folk enthusiasts do) would be
1) Collectively owned
2) Collectively and successively modified over time.

I appreciate, of course, that a lot of people have totally different definitions of the word (see a million threads and books on the subject). Most of these other defintiions do nothing for me. eg defining stuff as folk because it is "played on folk insruments"(whatever they are), or "because it is played in folk clubs" or "because I like it" or "because I put it on youtube". These are all definitions which have been advocated here, but I find them uninformative and of no use to me. So, I don't use them.