A handwritten book from late Antiquity or the Middle Ages is called a codex, which is the Latin word for book. The correct Latin plural is codices, although codexes is also often used. The codex was an improvement over the scroll, because its pages and a spine allow easier reading and can be written on both sides. Though early codexes were made with papyrus, medieval book makers used parchment or vellum (fine calf skin) for their pages, which made them very durable, but extremely expensive. The scholarly study of manuscripts from the point of view of book-making is called codicology.
A legal text or code of conduct is sometimes called a codex (or is it?).
See also : paleography.