SEALED = Factory sealed CD.
M = Mint condition. We only rate "M" if the CD playing surface is pristine with no visible playing surface flaws.
NM = The CD playing surface has one or two very minor imperfections that preclude it from being graded Mint.
NM- = Slightly more imperfections than NM that have no effect on playback.
VG+ = Incrementally more imperfections than NM- that have effect on playback.
VG = Incrementally more imperfections than VG+ that have no effect on playback.
VG- = A fair (but in no way heavy) amount of minor imperfections that have no effect on playback.