the blank leaves at the beginning and end of a book, pasted to the inside front and back covers and first and last pages.
Before books were mass-produced, it was common for endpapers to include maps, marbling, or other ornament. Endpapers are functional and serve to help support and strenthen the book, but they can also be quite beautiful. These examples are from books held in the D’Youville College Archives:
Although today most endpapers are blank, children’s books, in particular picture books, often still contain ornamented endpapers: