For the longest time, the term graphic novel
was the phrase used for any kind of longer comic book, hard or soft cover. They fell into two categories. One was a collection of previously published material from a comic series and usually had some kind of theme to it. The collected works of Jack Kirby or a story arc of Spider-Man, something like that. The other category were those graphic novels that were never published as a comic book, but where originated to be in the longer graphic novel format. Will Eisner
was the pioneer in this, and is considered the father of the graphic novel with such works as "A Contract With God", "Last Day in Vietnam", and "The Plot: The Secret Story of the Protocols of the Elders of Zion".
Lately, a new term has surfaced to describe those comics that have been created solely to be published in the graphic novel format - OGN, or original graphic novel. This describes any work that has been created with the intent to be published in the graphic novel format and was not previously published as a serial comic book.
Did you check out the new OGN by Joe Sacco? It is fantastic!