noun. A folded insert or section, as of a cover, whose full size exceeds that of the regular page.

noun. A piece or part, as of furniture, that folds out or down from a closed position.

noun. A gatefold

adjective. That folds out from a closed position

noun. an oversize page that is folded in to a book or magazine

"Christopher Tolkien has drawn a new map for the book, a tipped-in foldout on sturdy paper that should serve as an exemplar for all other publishers of books containing maps."

page  

centerfold  centrefold  

flip-top  fold-down  fold-out  port  psychiatrists'