The glossary provided by Diamond Comics defines graphic novels as follows:
A comic book that is longer in format than a pamphlet, and typically contains a complete story unto itself. Graphic novels usually have higher production values than the typical stapled comic book – they may be squarebound, for example, with cardstock covers. Some may be hardcover volumes. Although a graphic novel usually stands on its own as a complete story, it is possible to have a ongoing series or limited series of graphic novels telling a single story or series of related stories.
Cartoonist Jessica Abel provides this graphic definition.