A cover is something that protects, hides from view, embraces, or encompasses something else.
A cover is the top sheet of a bed.
A book's title page is a page at or near the front which displays its title. It is usually a recto page, i.e. on the right-hand-side in Western books that are written from left to right.
An illustration facing a book's title page is called frontispiece. The term frontispiece is also used in architecture referring to elements that frame and decorate the main, or front, door to a building.