M Mint Unused  &   Perfect  -  looks  as  if  just  printed.
NM Near Mint Like mint,  but very  slight  signs of  aging or handling - Unused.
EX
Excellent
No bends,  creases or marks on front of card - may be postally used.
VG Very Good Slight corner rounding, minor creasing or bending that is almost undetectable. 
G Good Corners  may  be  blunt  or  rounded.  May  have minor bends or creases,  flaking at  edges  or blemishes.  
Avg Average Shows significant wear and/or faults, potentially including severely rounded corners, general soiling, minor tears at edges or surface scrapes, one major crease or general light creasing, blemishes or postal markings which affect the image.
P Poor Card shows major wear or damage.