Grading Scale For Describing Condition

This scale is to distinguish books in collectible condition.
Most used papaperbacks are not in collectible condition and would be graded VG or worse.

These terms describe the most common signs of light wear - reading creases.
  reading crease on cover - the crease line on the front cover, going along the spine, from opening the cover
  reading crease on spine - the crease line up and down the spine from opening the book

Near Mint (NM) Almost perfect. There will be no reading creases on the spine or the cover. Any defects will be very, very minor in nature.
Very Fine (VF) Slight wear is beginning to show. There may be a light reading crease on the spine. All aspects of the book will be clean and fresh with no major signs of wear anywhere. There may be very minor color flaking or rubbing along a few edges.
Fine (FN) Book may have been read carefully several times. There may be a light reading crease on both the spine and the cover. There will be no creases or bends on the front cover beyond a reading crease along the spine. Light wear, minor color flaking, or minor rubbing noticeable on the extremities. Corners can be lightly bumped, with chipping and color flaking along edges.
About Fine (AFN) This is a book that is very nice but with wear on the cover. The spine is presentable but the cover has some minor wear, either a light crease or rubbing. It is a book that would grade as FINE or VERY FINE if the cover did not have the crease or the rubbing.
Very Good (VG) An obviously read copy, but still fairly tight. There is reading creases on the spine and the cover, and there are light creases on the cover. These may be stress lines or creases. There are wear spots, chipping and rubbing is noticeable but not major.
Good (G) A worn out, used copy that is complete. Cover has bends, creases, and is faded. This is a reading copy only.