What is a reverse side title of a page?

A page is a page you can read. A leaf is a sheet of paper with two pages able to be printed on it. A title page is the important first page with the name of the book and author. The back side of the leaf is the "verso". The back side of the title page is the verso of the title page, or if you want to be really picky you can say the verso of the title leaf.