Graphic Design encompasses many different elements that go into a successful website, for this article, we will keep it plain and simple. In other words, Graphic Design has more to do with the aesthetics and the look and feel of a website, including the menu system which links all of the pages in a clients site, seamlessly together so it flows without much thought to the end user, and is a pleasure to navigate through as it will also make sense to the visitor.
Wikipedia Graphic Design - full article - Graphic design is the process of visual communication and problem-solving using one or more of typography, photography and illustration. The field is considered a subset of visual communication and communication design, but sometimes the term "graphic design" is used synonymously. Graphic designers create and combine symbols, images and text to form visual representations of ideas and messages. They use typography, visual arts and page layout techniques to create visual compositions. Common uses of graphic design include corporate design (logos and branding), editorial design (magazines, newspapers and books), wayfinding or environmental design, advertising, web design, communication design, product packaging and signage.
Without proper Graphic Design, a website would look sophomoric and be clumsy to your visitors. A well designed website must look inviting and draw the visitor into navigating and absorbing the available content on the site. Therefore if the graphic elements within a website are not properly set to flow and provide the information that the visitor is looking for, it will create subtle negatives that even the visitor may not be conscience of, and generally the user will lose interest and leave a site and go searching for "what they are looking for". This may be your products and or the services that you offer, and they must be presented to the visitor with grace and subtlety while placating their need for information on how to engage you and your product or services.