folio; sheet folded in two
Refers to a single sheet of paper folded once to make two leaves (four pages). Used in bookbinding, printing, and stationery contexts.
This book is bound by stacking folio sheets.
Submit the manuscript to the printer in folio format.
A folded section or signature in bookbinding; 二枚折り can be one type of 折り丁.
Compound of 二枚 (two sheets) + 折り (folding), literally 'two-sheet fold'. The term is transparent and describes the result of folding one sheet into two leaves.