New: A book in Brand New condition to us is a book that is straight out of the box with no signs of reading or handling

Like New: A book in Like New condition is one which looks new but may have been on the shelf for a while before you get it.  May have some storage marks

Very Good: A book in Very Good condition is a book which has been read at least once.  It may have a folded over page mark or very slightly discolored non-binding side page edges, but will always look close to new at first glance.  There may be a couple of creased corners on pages.

Good: A book in Good condition is a book which has seen a little wear and tear, though is not in any way unusable.  The book is functionally whole, but the binding side may be worn from use or the pages may be folded over.  A book in Good condition will never be in disarray or falling apart, it will have all of its pages and will be very readable.  It will be noticeably used though.

Acceptable: A book in Acceptable condition is one in which you can visibly tell it is used, but still has its original shape and a good binding.  Acceptable means something which can withstand a few more readings without coming apart.  Pages can be folded over for bookmarks, and edges can be slightly discolored, but overall the book must be functional and capable of being read.  The cover may have slight damage but damage will be noted in listing.