1. Hist. A leaf of a paper or parchment, numbered only on the front. • A folio includes both sides of the leaf, or two pages, with the letters “a” and “b” (or “r” and “v,” signifying recto and verso) added to show which of the two pages was intended.
2. Hist. A certain number of words in a legal document, used as a method of measurement. • In England, 72 or 90 words formed a folio; in the United States, 100 words. — folio, vb.
“Folio … [a] certain number of words; in conveyances, etc., and proceedings in the High Court amounting to seventy-two, and in parliamentary proceedings to ninety.” Ivan Horniman, Wharton’s Law Lexicon 368 (13th ed. 1925).
3. A page number on a printed book.
4. A large book the pages of which are formed by folding a sheet of paper only once in the binding to form two leaves, making available four pages (both sides of each leaf).
