Of course words do have meaning, which is how language works. Some meanings are relatively fixed; if we say Dog we have a fair idea of the sort of thing we're on about (overly sycophantic quadroped noted for the stench and generosity of its faeces) - but if we say God, then we're apt to come unstuck. In the specifics of musical genres things are pretty clear too - if I buy a record of Gagaku I know pretty much what I'm in for, likewise Piobaireachd or Rebetika. Folk, on the other hand, like God, is a loose fitting mutable generality wide enough to accomodate a multitude of possibilities - including Moulettes, Marling, & Mumford, and a good deal more besides - all of whom clearly have roots in the Folk Aesthetic of the last 100 years (and all that involves) and are using that how they see fit.