glueman is right, there is no single definition. I play tunes (on the fiddle [electric] and mandolin [electric]) The very fact that I play electric instruments rather than acoustic condemns me in some people's eyes, but you know what ? I gave up caring along time ago. I play the way I play regardless of the origin of the tune. Infact I committed heresey last Saturday night, I accompanied a friend while he sang a few Ray Davies songs (the last of the great folkies:-D) It was fun. I operate, musically with no borders, it's the best way, you don't get all tangled up on dogma that way.