an individual leaf of paper or parchment, either loose as one of a series or forming part of a bound volume, which is numbered on the recto or front side only (仅在正面标号的)一张纸;一张羊皮纸书稿 ■the page number in a printed book (书的)页码 ■a sheet of paper folded once to form two leaves (four pages) of a book 对折纸,对开纸 ■a size of book made up of such sheets 对开本 imperial folio. 皇家对开本。 copies in folio. 对开本书册。 ■a book or manuscript made up of sheets of paper folded in such a way; a volume of the largest standard size 对开本书(或抄本);最大号对开本 old vellum-bound folios. 古老的犊皮装订对开本。 [as modifier]a folio volume. 一个对开本。
语源
late Middle English: from Latin, ablative of folium 'leaf', in medieval Latin used in references to mean on leaf so-and-so'. The original sense of in folio (from Italian in foglio) was 'in the form of a full-sized sheet or leaf folded once' (designating the largest size of book)