A graphic novel contains a beginning, a middle and an end. A graphic novel will offer the kind of resolution you expect from a novel, even if it is part of a series. Indeed, this makes a graphic novel longer and more substantive than a comic book, which is a serialized extract from a larger narrative. Calling something a graphic novel isn't just an elegant way of saying “comic”.
There is a very clear difference between the two. Graphic novels are much longer and tend to be much more complex. While a comic book tells a story about many subjects, graphic novels usually have their stories wrapped in just one or two books. Comics and graphic novels are very similar but very different at the same time.
Publishers also sometimes publish comic strips as a collection in book form, which causes a bit of confusion when trying to make a distinction. The division between graphic novelists and comic book writers is often comparable to the perceived difference between artists and artists. I think a key difference is that graphic novels tend to resemble real stories to the extent that they are capable of distorting history and facts in the minds of the less educated, while comics are clearly from another world. Some popular comics include Batman, The Incredible Hulk, Superman, The X-men, Wonder Woman and The Fantastic Four.
People often think that comics are aimed specifically at children or teenagers, although many adults also like the themes. Comics are periodical publications that are published monthly, and each edition contains excerpts from a general plot arc that takes months to complete. Most cartoonists like Art Spiegelman, Dan Clowes, Chris Ware and Jeffery Brown have said that they make comics. Knowing the background of comics and graphic novels helps you understand how these books became what they are today.
Comics are serialized stories; most are relatively short and tell the story of the book's heroes and heroines over a long period of time. A comic is a publication that contains sequential juxtaposed panels to represent the individual scene in comic book art. Graphic novels earned a reputation for being stark, explicit and for a mature audience, while comics were relegated to more popular popularity. A standard comic usually includes the beginning, middle, or end of a story, so a person usually can't read or buy just one to learn the whole plot or discover the characters.
Ironically, comics have long had their own stigma of being a childish pleasure, immature and guilty at best. You'll also notice that comics use staples to hold pages together, a binding method known as saddle stitching. Several comic book authors argue that the distinction is just a marketing term designed to sell the most expensive format.