Association

In their strictest sense "association copies" are books that were owned or inscribed to someone connected with the author and/or the particular book: often gifted from the other author to a notable friend. More broadly the term is applied to books owned by anybody notable, whether they were connected to the book, or author, or not connected at all. The reliable way of determing this is that the book will be signed or inscribed by that person, or have their particular bookplate.