endpaper
book page that consists of a double-size sheet folded, with one half pasted against an inside cover and the other serving as the first free page
en-GB/ɛndpeɪpə/
en-US/ˈɛndˌpeɪpɚ/
book page that consists of a double-size sheet folded, with one half pasted against an inside cover and the other serving as the first free page