Does anyone know?
SouNd Register fits, but I think NR is too terse for people unfamiliar with the hardware.
I'm not sure about this one, but looks like those register names are for GB/GBC dev.
On the GBA, the sound registers are named differently (and even worse heh) - see The Audio Advance
Each channel is controlled by multiple 16-bit registers, and the convention is like so:
SOUND<n>CNT_L = sound channel <n> control (Low register)
SOUND<n>CNT_H = sound channel <n> control (High register)
SOUND<n>CNT_X = sound channel <n> control (eXtra register) (doesn't exist for every channel)
Unfortunately these tell you nothing about what the register does... you just have to know that SOUND2CNT_L does the same thing as SOUND1CNT_H, because SOUND1CNT_L is taken by the sweep feature that only exists for channel 1 (and consequently channel 2 has no _X register).
This has prompted many people to try coming up with better names, which of course nobody can agree on, so it looks like we're stuck with these :')
Well, I hope it isn't so bad that there are ambiguous names floating around, which mean one register to one person and a different register to someone else.
If there aren't any like that, we could put a big table together with all the different naming standards so people can lookup the register address and see the name for their preferred style.