The Collaborative International Dictionary of English v.0.48:

mint state \mint state\ n. (Numismatics)
   A numerical grade indicating the degree of perfection of the
   condition of a coin which is classified as uncirculated,
   ranging from 70 for a coin in perfect condition to 60 for a
   coin which is uncirculated but may have a weak strike, or
   numerous small scratches from being handled in mint bags;
   usually used as the abbreviation MS; as, an MS-67 Morgan
   Dollar.
   [PJC]