This excerpt taken from the GOOG 10-K filed Feb 13, 2009.
Display advertising is internet advertising that typically includes static or animated images as well as interactive audio or video media, such as the banner ads you see on the tops or sides of many popular web sites. Our goal is to make it easy for anyone to use display advertising. We want advertisers to realize a better return on their display advertising campaigns and publishers to maximize the value of the content on their web sites by providing tools, platforms and channels for ad management and delivery.
We completed our acquisition of DoubleClick in March 2008 and are in the process of integrating DoubleClicks online ad serving and management services into Googles advertising solutions. DoubleClick provides Google with a platform for delivering display advertising. DoubleClick also provides services related to the delivery of display advertising, including media planning, buying, implementation and measurement tools for advertisers and agencies and forecasting and reporting tools for publishers. Through these tools we also provide publishers with access to agencies and advertisers to help them sell their advertising inventory and ways to streamline the ad sales process.
We also offer advertising solutions on YouTube in a range of video, static or animated images, and interactive formats.