I'll try to explain (hopefully I'm right).
An individual comic that you buy at the store is called an issue, e.g. "Walking Dead #1" is the first issue of the entire series. These are what we traditionally call "comic books."
They then collect issues into "books" or "volumes" of several issues (eight or so, I think). The book you linked above is one of those.
They then collect the books into compendiums. So compendium one has books 1-8 in it, which covers issues 1-48.
That being said, there are several spinoffs that are outside the numeration of the traditional "The Walking Dead" series, though I'm not sure that any of them are actually graphic novels.
The Rise of the Governor is one of these, and it's a traditional prose novel (no pictures).
Oh to make matters even more confusing, they have what is called an
"Omnibus" that is basically a volume/book set up to be more like a collector's edition. Hardbound reproduction of the original comics with their covers and such in a slipcase.