Used books and games come into the shop in a variety of conditions. We give them a general code that represents the overall condition grade, and then supply specifics in the item notes as needed.
New: Just like it sounds. There may be a trivial amount of shelfwear.
Like New (Fine): An apparently unused copy in near-perfect condition. Some slight flaw prevents this item from being called "New" -- shrinkwrap missing, a small corner bump, a hint of wear, and the like. Suitable for presenting as a gift.
Very Good: A copy that has been used, but was well-treated, and remains in excellent condition. Pages are intact and are not marred by notes or highlighting. A book's spine remains undamaged. A box set may have light edge/corner wear, a touch of lid dishing.
Good+: Has a bit too much wear, or some notable flaw, to be Very Good, but still possibly collector-grade.
Good: An average used copy. In a book, this is a "Reading Copy" and for an RPG, a "Play Copy." Pages can include limited notes and highlighting, but should not obscure text.
Acceptable (Fair): A readable/usable copy, but this is its last journey. Will have considerable wear or a non-essential component may be missing from an RPG set.