A repair to a book, where the original spine has been replaced. If the original spine or backstrip can be salvaged, it might be glued down on the new spine. The result of the latter is found in bookseller’s catalogs thus: “Rebacked, with the original spine laid down (or laid on or retained).” Can be considered a defect, i.e., there is original material that has been lost. However, an expertly repaired volume can be worth more than the book in its original but unrepaired condition.
The book pictured has been skillfully rebacked while retaining the original boards. Note the color of the new spine cloth matches the existing red quite closely. The spine labels are new as no part of the spine was present when the rebacking was done.