EXCELLENT:
This is a new part that is still in the package and in perfect condition.
VERY GOOD:
This is a new or used part that may have some minor scratches, but is otherwise in perfect working order.
GOOD:
This is a used part that is in good working order. It may have some surface scratches, but no mechanical problems.
FAIRLY GOOD:
This is a used part that is in good working order but has a larger amount of cosmetic damage. Or it is a part with a small mechanical problem but is still useable.
FAIR:
This is a used part that may not be in very good working order or has some cosmetic damage. It is still a useable part.
POOR:
This part has a lot of cosmetic damage and or may not be in working order.