fo·li·o (fō'lē-ō') – noun

Pronunciation: foh-lee-oh
Plural: fo-li-os. Adjective, verb, -li·oed, -li·o·ing.

1. a sheet of paper folded once to make two leaves, or four pages, of a book or manuscript.

2. (in a book) the number of each page. The even folios are on the left-hand pages (verso) and the odd folios are on the right-hand pages (recto).

3. a sheet of any written or printed material (especially in a manuscript or book).

Origin: late Middle English, 15th century, 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 the book.