Unlike search advertising, which utilizes the search network (search engine websites), display advertising utilizes a larger network known as the display network (third-party non-search engine websites). This network is composed of websites organized thematically. Display advertising is managed much like traditional search advertising, but the presentation of your ad differs. Rather than rely only on text, display advertising provides the flexibility to combine creative visuals with your ad. You then have the ability to target these ads at websites that match your theme.
The display network is composed of third-party websites (e.g. forbes.com, espn.com, etc.), that boast high traffic volume. By joining Google’s display network, these sites can earn extra revenue by presenting ads to their visitors in hopes of getting a click, and a share of the cost per click.