... is not an album by
Led Zeppelin. Led Zeppelin's fourth
album is officially
untitled, with the only markings on it being the four
runes that each
member of Led Zeppelin chose for themselves. They chose this course of action because they wanted their music to sell albums, not the name Led Zeppelin.
The album continues to be called four only because (1) it's their fourth album, and (2) because their first three albums were titled Led Zeppelin, Led Zeppelin II, and Led Zeppelin III. But it's not Led Zeppelin IV. It doesn't have a title.