Simply put, a graphic designer is a professional that works in the graphic design industry.
For those of you who are looking for a more detailed answer, graphic designers work with images as well as text in order to design and create visually appealing elements, including brochures, logos, advertisements, and websites. In order to create these items, graphic designers will often work with a variety of different types of images, including photographs, paintings, and digital media. Photo and image editing software is often used to manipulate images and create the designs.
Not only do these artists need to make their creations look great, they also usually need to make their creations speak in a way. Most clients hire graphic designers to create something that sends a message. Sometimes this message is loud and clear, but other times it is meant to be subliminal.
Source: The Art Career Project