International Online Booksellers Association Condition Definitions:
As New; Fine: Without faults or defects.
Near Fine: A book approaching FINE (or AS NEW) but with a couple of very minor defects or faults, which must be noted.
Very Good: A book showing some signs of wear. Any defects or faults must be noted.
Good: The average used book that is totally complete (as issued) and intact. Any defects must be noted.
Fair: A worn book that has complete text pages (including those with maps or plates) but may lack endpapers, half-title page, etc. Any defects or faults must be noted.
Poor or Reading Copy: A book that is sufficiently worn that it's only merit is the complete text, which must be legible. Any missing maps or plates must be noted. May be soiled, scuffed, stained, or spotted, and may have loose joints, hinges, pages, etc.
Ex-Library: Must always be designated as such no matter what the condition of the book.
Book Club: Must always be noted as such no matter what the condition of the book.
Binding Copy: A book in which the text block, including illustrations, is complete but the binding is lacking, or in such poor condition it is beyond realistic restoration efforts.
Remainder Marks, Bookplates, Previous Owner's Name: These are faults and must also be noted if they apply.