Type of page which is larger than the others in a
publication and thus must be folded to make it the same size as the
covers in the same way as a
centerfold, except the gatefold can be found anywhere in the publication.
Also said of LP sleeves that open up like books, with the vinyl stored in the covers. Further elaboration on the gatefold concept include the three-segmented gatefold, either Z-folded or spiral-folded, and the four-segmented double gatefold.
Of course, compact discs also have gatefolds, but mostly for pragmatic purposes - for multiple-disc albums. However, on some cardboard CD boxes (The K&D Sessions, Björk's Homogenic and LTJ Bukem's Journey Inwards et al) you get one or two extra segments depending on the type of fold.