Grading convention is sleeve/vinyl.
Herewith, my understanding of grades, and a description of each from Record Collector:
The record itself is in brand new condition with no surface marks or deterioration in sound quality. The cover and any extra items such as the lyric sheet, booklet or poster are in perfect condition. Records advertised as Sealed or Unplayed should be Mint.
The record shows some signs of having been played, but there is very little lessening in sound quality. The cover and packaging might have slight wear and/or creasing.
The record has obviously been played many times, but displays no major deterioration in sound quality, despite noticeable surface marks and the occasional light scratch. Normal wear and tear on the cover or extra items, without any major defects, is acceptable.
The record has been played so much that the sound quality has noticeably deteriorated, perhaps with some distortion and mild scratches. The cover and contents suffer from folding, scuffing of edges, spine splits, discoloration, etc.
The record is still just playable but has not been cared for properly and displays considerable surface noise; it may even jump. The cover and contents will be badly damaged or partly missing.
The record will not play properly due to scratches, bad surface noise, etc. The cover and contents will be badly damaged or partly missing.
The record is unplayable or might even be broken, and is only of use as a collection-filler.
I hate grade inflation. VG should indicate very good, not 'crap'.
If you find yourself using many gradations of not-quite-stone-cold-perfect (I'm lookin' at you, VG+++), give your records a hard look. There is no shame in an honest grade. You and any potential counterparties will benefit. I have been happy to acquire records in fair shape. They remain a pleasure to play, because the alternative, usually, is not to hear them at all.