As New

This is used only when the book is in the same immaculate condition to which it was published. There will normally be no defects, no missing pages, no library stamps, etc.

Fine (F or FN)

Approaches the condition of As New, but without being crisp. For the use of the term Fine, there will normally be no defects, but any defect will be noted.

Very Good (VG)

Describes a book that does show some small signs of wear - but no tears - on either binding or paper. Any defects will be noted.

Good (G)

Describes the average used worn book that has all pages or leaves present. 

Fair

Worn book that has complete text pages (including those with maps or plates) but may lack endpapers, half-title, etc. (which must be noted).  All defects will  normally be noted.

Poor

Describes a book that is sufficiently worn but normally has the complete text. The copy may be soiled, scuffed, stained or spotted and may have loose joints, hinges, pages, etc.