Graphic novels, manga, and comics are formats, not genres.

Comics:
"Juxtaposed pictorial and other images in deliberate sequence, intended to convey information and/or to produce an aesthetic response in the viewer" (Scott McCloud, "Understanding Comics, 1993).
Graphic Novel
A story that is presented in comic strip format and published as a book. A graphic novel can best be described as being book-length in format, containing sequential art narrative. It shares many of the characteristics of prose novels, including a beginning, a middle, and an end. The story is presented through the combined use of image and word.
There are five different types of graphic novels:
- Manga
- Superhero stories
- Non-superhero stories
- Personal narratives
- Nonfiction
Manga
Manga (mahn-ga, literally "whimsical pictures") refers to comics originally written and published in Japan. Most manga begin as serial chapters published in Japanese graphic magazines such as Weekly Shonen Jump and Shojo Beat. If a series is popular enough, chapters are then collected and republished as paperback books called "tankobons" or volumes.