Mint Sealed (MS): No noticable defects and sealed in original factory or store shrinkwrap or sticker.

Near Mint (NM): No noticable defects, but not sealed.

Fine (F): One or two slight defects that prevent a Near Mint rating.

Very Good (VG): More than one or two slight defects. Still in acceptable condition.

Good (G): More severe defects (box slightly torn or crushed; noticable wear on media, manual, or other materials).

Excess Defects (ED): Excessive and / or unusable defects (crushed, ripped, or sheared box; torn manual pages; box or manual written on in marker, etc.).

Modifiers:
Sealed (S): Sealed with original factory (or store) shrinkwrap or sticker. Not to be confused with a re-wrapped previously-opened box.

Compressed (C): Package has been crushed or compressed.

Torn Wrap (T): Sealed package has tears in the shrinkwrap.

Item Missing (IM): Package is incomplete, missing one or more items from the original distribution.

Missing Minor Component (MMC): Package is missing a minor component (warranty or registration card).

Bad Media (BM): Media (diskette, CDROM, tape) is known to be bad or defective.

Complete MobyScale notes, with examples