I use the most usual internationally prooven grading system, which was developed by Goldmine Magazine originally for vinyl.
Here are the short version.
SS / Still Sealed
Never opened. Flawless, with no damage whatsoever. Might be Sealed or Not dependend on the manufacturer.
NM / Near Mint
Vinyl: nearly perfect. A very minor scuff and very little else can appear on the vinyl. This will most likely have occurred during packaging, or removing the record from the inner sleeve but had been handled with extreme care.
EX / Excellent
Vinyl: an excellent condition for vinyl will allow minor scuffs which are visible but only slightly.
VG+ / Very Good+
Vinyl: may have scuff marks and signs of some wear but will still play almost perfectly throughout, with only "barely detectable" crackles or pops. A slight noise at the begining is allowable, but the remainder must be nearly flawless. Definitely no scratches or gouges that a touch with a dry finger can feel.
VG / Very Good
Vinyl: may crackle, pop or make other annoying noises, but only occasionally,never continuously, and not more loudly than the music being listened to
G / Good
Vinyl: may have continuous low level crackles, pops, etc... but not so loud as to make the music completely unlistenable or unenjoyable to the casual listener. Might also have "nasty little scratch" causing popping on one or two more songs, with the rest of record playing fine.
F / Fair
Vinyl: mostly quiet noisy the whole way through, might have heavy scratches and might even skip.
P / Poor
Vinyl: only one or two songs on the whole album are playable.
none / missing