As New:  The book is in the same immaculate condition as when it was published.  This could be the description for a book that has been kept in a warehouse for years, never shelved, thumbed, or even opened yet may still be some years old.

Fine (F or FN): A Fine book approaches the condition of As New, but without being crisp.  FN means Near Fine. The book may have been opened and read, but there are no defects to the book, jacket, or pages.  

Very Good (VG): Describes a book that shows some small signs of wear - but no tears - on either binding or paper.

Good (G): Describes the average used-worn book that has all pages or leaves present. 

Fair: A worn book that has complete text pages (including those with maps or plates) but may lack endpapers, half-title, etc. (which must be noted). Binding, jacket (if any), etc., may also be worn.

Poor: Describes a book that is sufficiently worn.  Any missing maps or plates should still be noted. This copy may be soiled, scuffed, stained, or spotted and may have loose joints, hinges, pages, etc.

Binding Copy: Describes a book in which the pages or leaves are perfect but the binding is very bad, loose, off, or non-existent.

Reading Copy: A copy of a book usually in poor to fair condition that includes all text presented in a legible fashion.  The copy is fine to read but nothing more.