flutter book
OAB Definition
structure of single folios tipped together at the fore-edge, creating an accordion of stiff, glued peaks (nori-ire gajo), with a cover tipped onto the first and last pages. The book can be read like a codex but has a loose spine so the text block can be expanded for display. The text block may tumble, or flutter during use.
ABT Definition
Case-bound books featuring an accordion-folded text block that is attached to the front and back covers but not to the spine, so that the pages fall forward or flutter.