"Juxtaposed pictorial and other images in deliberate sequence, intended to convey information and/or to produce an aesthetic response in the viewer" (Understanding Comics, Scott McCloud).
(From McCloud's Understanding Comics)
McCloud also refers to comics as "sequential art," or panels containing a combination of images and words that are set in a specific sequence to tell a story.
Check out the following interview of Scott McCloud. He discusses a lot about his view of comics.
"I try to learn from everyone... I try to follow no one..." --- Scott McCloud