music, the music of a zone area and instance
ambiance, special effect sounds ( i think)
sound, spell sounds, npv voices, damange sounds ect
the 3 options we have for sound ingame.
i like hearing the boss voices, but some times its hard to hear them over the clang and bang of attacks. i wish blizz would seperate the too. adding a npc voice option instead of having it included with every other sound in a raid would make thing a bit better for me. i like hearing boss quotes :P