How many letters does the top answer for “an oversize page that is folded in to a book or magazine” have?

The most common answer is foldout (7 letters).

Crossword clue: an oversize page that is folded in to a book or magazine

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

foldout 7 letters wn-def

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

gatefold 8 letters wn-def

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