Concept
Recto is the "right" or "front" side and verso is the "left" or "back" side when text is written or printed on a leaf of paper (folium) in a bound item such as a codex, book, broadsheet, or pamphlet. In double-sided printing, each leaf has two pages - front and back. In modern books, the physical sheets of paper are stacked and folded in half, producing two leaves and four pages for each sheet. For example, the outer sheet in a 16-page book will have one leaf with pages 1 (recto) and 2 (verso), and another leaf with pages 15 (recto) and 16 (verso). Pages 1 and 16, for example, are printed on the same side of the physical sheet of paper, combining recto and verso sides of different leaves. The number of pages in a book using this binding technique must thus be a multiple of four, and the number of leaves must be a multiple of two, but unused pages are typically left unnumbered and uncounted. A sheet folded in this manner is known as a folio, a word also used for a book or pamphlet made with this technique. Loose leaf paper consists of unbound leaves. Sometimes single-sided or blank leaves are used for numbering or counting and abbreviated "l." instead of "p." for the number of pages. The terms are shortened from Latin: rēctō foliō and versō foliō (which translate as "on the right side of the leaf" and "on the back side of the leaf"). The two opposite pages themselves are called folium rēctum and folium versum in Latin, and the ablative rēctō, versō already imply that the text on the page (and not the physical page itself) are referred to. In codicology, each physical sheet (folium, abbreviated fol. or f.) of a manuscript is numbered, and the sides are referred to as folium rēctum and folium versum, abbreviated as r and v respectively. Editions of manuscripts will thus mark the position of text in the original manuscript in the form fol. 1r, sometimes with the r and v in superscript, as in 1r, or with a superscript o indicating the ablative rēctō foliō, versō, as in 1ro.
