The grading definitions below are based on the Goldmine Magazine standard.
It is widely accepted as the standard for record collectors worldwide.

Cover/Record

All records are visually graded and/or spot played

SEALED
In factory fresh condition. May have some portion of the shrink wrap torn away, but essentially upopened. Any physical damage on a SEALED LP will be noted. May have original price and/or feature stickers still affixed.

M (Mint)
A Mint album is absolutely perfect in every way! Since nothing in this world is perfect (including our record grading skills), we don't use Mint.

NM (Near Mint)
A nearly perfect record. The record shows no obvious sign of wear. The cover has no creases, folds, seam splits or any other noticeable similar defect. No cutout holes, notches or cutcorners either. The same applies to any inserts, such as posters, lyric sleeves, and the like. Basically, Near Mint looks as if you just got it home from a new record store and removed the shrink wrap.

VG+ (Very Good Plus)
Shows some signs that it was played and otherwise handled by a previous owner who took good care of it. Record surfaces may show some slight signs of wear and may have slight scuffs or very light surfaces scratches that don't affect one's listening experience. Very slight warps that do not affect play are may be evident. The label may have some ring wear or discoloration, but will be barely noticeable. The cover may have slight signs of wear and may be marred by a cutout hole, notch or cutcorner indicating it was taken out of print and sold at a discount. In general, if not for a couple of minor things wrong with it, this would be Near Mint. All but the most mint-crazy collectors will find a Very Good Plus record highly acceptable for their collection.

VG (Very Good)
Many of the defects found in a VG+ record are more pronounced in a VG disc. Some surface noise may be evident upon playing, especially in soft passages, between tracks or at the lead-in grooves, but will not overpower the music. Groove wear will start to be noticeable, as will light scratches (just deep enough to feel with a fingernail) that may affect the sound. The cover may be marred by writing, or have tape or stickers (or their residue) attached. The same may be true of the record labels. However, it will not have all of these problems at the same time.

G/G+ (Good/Good Plus)
Good does not mean bad! A record in Good or Good Plus condition can be put onto a turntable and will play through without skipping, but may have significant surface noise and scratches and visible groove wear. The cover may have some seam splits, especially at the bottom or on the spine. Tape, writing, ringwear or other defects will start to overwhelm the cover. If it's a common title, you'll probably find another copy in better shape eventually. But if it's something you have been seeking for years and the price is right, get it.

*** Abbreviations ***

coh = cutout (cover will have drill hole, cutcorner or sawcut)
imp = import
obi = paper belt wrapped around cover of many Japanese pressings
promo = promotional copy
quad = quadraphonic recording
re = reissue
soc = sticker on cover
sol = sticker on record label(s)
ss = still sealed
toc = tear on cover
ts = taped seams
woc = writing on cover
wlp = white label promotional issue lp
wol = writing on label(s)