a book made with large sheets of paper, especially as used in early printing （尤指早期印刷的）对开本 a folio edition 对开本, 对摺本
- (specialist)
a single sheet of paper from a book （书籍的）一页
Word Originlate 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).