From Google's blog today:
"We’re always focused on improving AdSense by bringing more advertisers to your sites, giving you more control over the ads that appear on your sites, and giving you more transparency into how much revenue you’re earning. Over the past year, much of our focus has been on attracting more display advertisers and display advertising spend to your sites. We’ve added new advertisers and introduced options that help these advertisers reach your sites. At the same time, advertisers have continued to run ads on YouTube and our own properties. To make our display media offerings clearer to advertisers and agencies so that we can continue to bring more display spend to your sites, we’re creating a new umbrella name for all these properties, the Google Display Network.
The Google Display Network will comprise all of the sites where advertisers can buy ads through Google, including the over one million AdSense and DoubleClick Ad Exchange partners as well as YouTube and Google properties such as Google Finance, Gmail, Google Maps, and Blogger. As an AdSense publisher you’re already part of the Google Display Network. We’re not making any changes to how AdSense works, so no action is required on your part. If you use AdSense for search, your AdSense for search ad space won't be part of the Google Display Network. Advertisers will continue to be able to purchase ads on your search results pages in the same way they always have."
Find out more about Google's Display Network.