Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

accordion-pleated fold

A method of folding endpapers so that the pleat provides a hinge at the inner joint of the cover. The pleat also provides for expansion to allow the covers to swing open freely and not exert strain on the first and last leaves of the book. In certain cases, however, it can also create a sharp, knife-like fold which, if wide enough, may cause a brittle leaf to bend sharply and crack at that point. (81 )