This post is in a forum called phpBB discussion.
That is in a category called Non-Support specific
The category is a section which has a common theme for the forums that are under it.
So in your example you would have a category called music
In that you could have forums called pop, rock, jazz
In those you can have as many subforums as you like.
But you have to think about usability. If you have to go more than 3 clicks from the index to get where you want to be, people generally find that confusing.
If you're thinking of having forums for pretty much every act out there, forget it. The dedicated fan sites already have that market covered. You're better off just have a music forum first. If you then get a lot of posts about pop, make a pop forum for those.
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