Graphic Design: The art and profession of selecting and arranging visual elements-such as typography, images, symbols, and colours-to convey a message to an audience. - Encyclopædia Britannica
I think that that may be just the beginning of what Graphic Design is, but it's as good a place to start as any. Graphic Design is to me a blending of Art and Communication. Creating an elegant and interesting framework with which to present information.
As a Graphic Designer I have to be both an artist who can visualize a design, and a technician who can bring that design to life. It is an odd combination of artistic inspiration and technical know-how, a graphical jack-of-all-trades.
I'm current doing Drupal development for Riven Design.