The Japanese version of my book had a sleeve (image) over the lower half of the book. I learned tonight from my Japanese publisher that this is an “obi”:

“Obi” literally means a band or belt you wear with a kimono. I am not sure whether such a thing exists in your country or not. It is slid over the lower part of the book cover. Usually “catch phrases” are written on it.”

Ok. Maybe useless trivia!