Gatefold
ahd-5
noun.
A foldout, especially one that opens to double the page size.
Wiktionary, Creative Commons Attribution/Share-Alike License
noun.
An
overlarge
page
that is
folded
into a
book
or
magazine
; a
foldout
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
noun.
an oversize page that is folded in to a book or magazine