Limp binding is a bookbinding method in which the book has flexible cloth, leather, vellum, or (rarely) paper sides.
The thongs could also be used at the fore edge of the covers to create a closure or tie.
[2] Some limp vellum bindings had yapp edges that flop over to protect the textblock.
[1] Its usage subsequently declined until "revived by the private presses near the end of the 19th century".
[1] From about 1775 to 1825, limp leather was commonly used for pocket books, but by the 1880s limp bindings came to be largely restricted to devotional books, diaries, and sentimental verse, sometimes with yapp edges.