String-of-leaves ~ scrolls ~ concertinas ~ codices. For many years I associated codex with ancient, written, archaeological finds. I was not wrong, but had completely missed the point that codices was descriptor of early binding techniques. Certainly from the selection at the start of this paragraph it is the most popular binding method ~ and it has been for centuries.
A folio is a piece of paper ~ or similar material ~ folded into half. When a folio is sewn to other folios ~ either tucked inside ~ or adjacent ~ or both ~ then that is codex binding ~ or codex sewing. Historians may wish to reserve the name for handwritten early books. It will beobvious to readers by now that I do not subscribe to that narrow definition.
Without the fold for the thread to link the pages together they have have to be joined ~ to make a book ~ by stab sewing  or gluing .