"a popular usage inclusive of many different styles, idioms, genres, approaches"

As far as "popular usage" goes, I fear you're being a tad optimistic with all those delightful variables! For anyone not already a folk fan (ie: the vast majority of word users), it pretty much means two things ie: 'fiddley diddley' or 'girl/bloke sitting on a stool while strumming an acoustic guitar'.