The term graphic novel should be simple: graphic refers to the images involved in the comics medium, and novel refers to a complete story originally published in a single binding.
The problem is, people tend to use the term to describe comics that don’t fall under this simple definition. The comics one usually thinks of when discussing graphic novels are:
- Maus (by Art Spiegelman)
- Watchmen (by Alan Moore and Dave Gibbons)
- Dark Knight Returns (by Frank Miller)
- The Sandman (by Neil Gaiman et al)
Of these, none are truly graphic “novels”. Maus (although originally published in a single binding) is more of biography or a memoir, and so shouldn’t be referred to as a “novel”. Watchmen was a 12-issue comic series. Dark Knight Returns was a 4-issue limited series. Sandman was an ongoing series which totaled out at 75 issues.
Ultimately, the term graphic novel has been used in so many ways that it can mean almost anything you want it to mean.
Personally, I prefer the term comics. It’s simple, it’s all encompassing, and the word has meant the same thing for at least a hundred years: the mixture of art and words laid out sequentially in panels.