Plural of folio: sheets of paper folded once to make four pages, or page numbers in a manuscript or book.
From Latin 'folium' (leaf), used to describe pages that were literally folded leaves of parchment or paper in early books.
Shakespeare's plays were first published in a 'First Folio' in 1623—a massive book with pages so big (about 9 x 12 inches) that scholars still track down original folios worth millions of dollars today.
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