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
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imperial folio 皇家对开本
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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
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old vellum-bound folios 古老的犊皮纸包边的对开本
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[as modifier]
a folio volume. 一本对开本。
"late Middle English： from Latin, ablative of