A publisher-authorized content correction that is made after a book has been printed and bound.
It can be as small as a scrap of paper to correct type, or as large as a page or a signature to correct a section.
The corrected page or illustration is glued onto the page or inserted into an already bound book.
They are less common today with the advanced printing techniques, but were very common in the 17th and 18th centuries due to numerous printer errors.
Also known as Cancels.