"Library knot" (visual definition)

"Tying with the library knot is a versatile and gentle way to secure materials that are fragile. It may also be used to tie intact materials, and, though the instructions show a bound volume, tying with the library knot is a standard way to bundle serial issues or multi-volume monographs together."

https://staff.library.wisc.edu/binding-unit/library-knot-instructions/