Can a graphic novel series follow a single story over many issues? Or are they all supposed to be self-contained stories?

I've heard that graphic novels do not follow a single story, but are self contained stories instead. A single story over many issues is actually a comic book. I can't help but compare graphic novels to manga, which follow a single story that's spread over many volumes. Can the same be said about graphic novels or would something like that be a comic book in the shape of a book (like how a graphic novel is)?