“ FOLIO (properly the ablative case of the Lat. folium, leaf, but also frequently an adaptation of the Ital. foglio) , a term in bibliography and printing, with reference either to the size of paper employed, or of the book, or to the pagination. In the phrase “in folio” it means a sheet of paper folded once, and thus a book bound up in sheets thus folded is a book of the largest size and is known as a “folio” (see Bibliography) . Similarly, “folio” is one of the sizes of paper adapted to be thus folded (see Paper) . ”