or end pa·per
a sheet of paper, often distinctively colored or ornamented, folded vertically once to form two leaves, one of which is pasted flat to the inside of the front or back cover of a book, with the other pasted to the inside edge of the first or last page to form a flyleaf.
Origin of endpaper
First recorded in 1810–20
Also called end leaf, end sheet.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
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
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012