Sealed: Jacket sealed shut in original factory shrink wrap; disc sold ungraded or "as is".
M= Mint: Open record with no (zero) flaws. This is rarely if ever used.
NM=Near Mint: Clean and glossy vinyl. May have one or two insignificant imperfections not affecting play, thus “Near” Mint. This also applies to labels and cover.
EX=Excellent (aka VG++): Still very glossy and nice. May have two or three insignificant imperfections (i.e. sleeve scuffs, faint hairline scratches, or other superficial marks) that will not affect play.
VG+=Very Good Plus: More visible imperfections than EX. These may include sleeve scuffs, light scratches, or other superficial marks. But no defects causing major issues on playback.
VG=Very Good: Same imperfections found on VG+ records but in slightly greater numbers. Records graded VG and above will typically not have any scratches that are deep enough to be felt with a fingernail. Record may play with some occasional light background noise in spots, never overpowering the music. 
VG-=Very Good Minus: A number of visible imperfections; the presence of a considerable number of light scratches will force a VG- grade, as will the presence of significant isolated defects such as scratches deep enough to be felt with a fingernail.
G=Good: Good does not mean bad! The record will still play through without skipping, so it can serve as filler until something better comes along. But it has significant surface noise and groove wear. Pervasive imperfections of varying degrees including both light scratches and scratches deep enough to be felt with a fingernail. G+ and G- are used to indicate stronger and weaker copies within this range.
All records are visually graded and only play graded when noted.