Graphic novels are like comics, but usually bound in a thicker format, and telling a complete story - rather than an issue at a time. Graphic novels can be about superheroes, yes, but they can also tell the story of the Civil Rights movement, the Holocaust, be a cookbook, or even talk about and show average people with normal lives.
Graphic novels usually break down into 5 categories:
The Saint Paul College Library has a dedicated Graphic Novel Collection.