folio
n. countablen. a large sheet of paper folded once to make two leaves of a book. It also refers to a book made of these large pages, which is usually very big and heavy.
n. a leaf of a manuscript or book, consisting of two pages (recto and verso). Often refers to a book format where sheets are folded once, resulting in a large physical volume.
The librarian carefully turned the fragile folio.
Scholars traveled from across the country to examine the original Shakespeare folio kept in the university's special collection.
The manuscript is organized by folio number rather than page number, a common practice in archival research when dealing with historical documents that predate modern printing standards.
From Middle English folio (“leaf of a book”), borrowed from Medieval Latin foliō, Late Latin foliō, Latin foliō, the ablative singular form of Late Latin folium (“leaf or sheet of paper”), Latin folium (“leaf of a plant”), ultimately from Proto-Indo-European *bʰleh₃- (“bloom, flower”). Doublet of foil and folium, and distantly related to phyllo and phyllon. Senses 1, 2, 3.1, 5, and 6 relating to a leaf or page are derived from Medieval Latin foliō in references; sense 5 (“page in an account book”) may be derived from Italian foglio (“rectangular sheet of paper”), from Latin folium. Senses 3.2 and 3.3 relating to a paper size are from Italian in foglio or its etymon Latin in foliō.
In modern accounting or law, it may refer to a page number in a ledger or a specific case file.