what is a 1 volume set?

[Darkpool]

here's the book I'm confused about.
http://www.goodreads.com/book/show/11...
So, what is a 1 volume set, apart from a really weird way to describe a single book? The edition in question appears to be large print. I'm itching to take "1 volume set" out of the title, because it's such a stupid descriptor, but thought I'd seek opinions from anyone who knows more about it than I do (ie, anyone) first... :-)

[Vicky]

I think it has to do with the fact that it's a ReadItHowYouWant Large Print Edition. They offer different font sizes, and I suspect a larger font size might make this book a multi-volume edition.

Don't think it's necessary though, I would specify if it were a multi-volume edition, but "1 volume set" is pretty silly.