either of two leaves at the front and back of a book pasted to the inside of the board covers and the first leaf of the book to secure the binding
endpaper in American English
(ˈɛndˌpeɪpər)
noun
a folded sheet of paper one half of which is pasted to the inside of either cover of a book, the other half to theinside edge of the first (or last) page of the book