A frontispiece is an illustration on one of a book's first pages, usually opposite the title page. Some editions of Winnie the Pooh include a map of the Hundred Acre Wood as a frontispiece.
Children's books and classics are most likely to have a frontispiece, which is considered a bit old-fashioned today. Your beloved copy of The Wind in the Willows or a collectible edition of Little Women probably include a frontispiece — and the volumes in your Harry Potter collection might as well. In architecture, a frontispiece is something that frames or decorates the entrance to a building. What these two kinds of frontispieces have in common is being located in the front of something.