I believe Hyrdomancer is correct. Comic is a single issue, but these days the comics are being compiled into a larger volume known as Graphic Novels. Using this instance, I have very few comics, because I wait until a chunk of issues are released into graphic novel format. Also, another difference I've noted, the comic issues have advertisements in them, whilst graphic novels do not, and many I've come across also have author introductions. So there are differences between them.
To be offended or angered by this and/or just use it as ammunition to bash North American culture is pretty low. Who really cares what they're called in the end. There's no need to justify reading them either, they have good stories in them, and good artwork.