Art is expression, graphic design is communication.
In art, generally the artist's goal is to express emotion through the chosen medium. Some might say "create beauty through the medium" but the goal is not always beauty, but nearly always expression.
In graphic design, the goal is to communicate visually. This too does not always involve beauty. It instead consists of conveying a message in the appropriate "accent." It is similar to a line spoken in a movie. If the actor delivers the line with the appropriate accent, diction, volume, timbre and emotion, you will understand the line as the script intends. In the same way, a graphic designer delivers a message using the appropriate typeface(s), size, style, colors, accompanying imagery, and layout to best convey the message to the intended audience.