the latter.
Grunge was basically a scene that grew around the noisy hard rock independent music scene that weren't a whole lot different from the likes of Husker Du or Dinosaur Jr., but people felt compelled to create a new genre that was pretty much completely meaningless. Kinda like emo, it even had its own fashion too!
This is some high-fidelity music nerd bullshit, but it's just one of those things that I feel I need to shit all over every time I see it because it's fucking retarded.
I'm not sure I think grunge was meaningless, though. The problem with emo is that it was completely arbitrary and unnecessary. It was just a silly differentiation and it didn't even represent a particular movement. I agree that most grunge acts sounded pretty close to stuff like Dinosaur Jr and that if they were just BANDS, there would be no need for grunge as a genre to exist, but it was this huge, city- and ultimately nation-wide movement that got far bigger than its influences ever had been. I kind of think of grunge as being an acceptable brand because I think once something gets to be that widespread, it's more acceptable to label it than if it is just a few bands doing something. Like, they could've called it indie rock in the same way their roots were ACTUAL indie rock, but I think classing that entire scene with all of its predecessors on the basis that they were musically very similar would have belied the size and the strength of the movement.
I think the same thing about post-punk, more or less; the large majority of bands in that genre could easily have been called indie rock in the very accurate sense of the term, because there isn't really a single POST-PUNK SOUND or anything, but I think certain genres like grunge/post-punk are based more around a certain event or period or movement than they are the qualities of the music itself. I'm alright with this! The problem I have with emo and indie is that emo was too small a difference and too little a movement to really justify considering it separately from hardcore or whatever, and indie isn't ANYTHING. It's not a movement, it's just a catch-all term for anything even remotely sub-mainstream.