Smaller numbers refer to even smaller books.
The condition of a book with dustjacket is often abbreviated in the form of two terms divided by a slash. As new or Mint - mint or as new condition means the book is without any defects in crisp, tight, and fresh conditon. Good is still a sound copy with all pages present but there are some major defects or soiling or considerable wear which hopefully is described. You should ask about the condition of a good copy. All text must be present and readable.