This just makes so much sense! As a publisher and Webmaster, you can tell your contextual ads, which content is the real content on the page. As you and I know, many content management systems default text into titles and meta information into the pages, that have nothing to do with the actual article on that page. By telling the contextual AdSense ads, what content is relevant to the page, AdSense can then serve up more contextually relevant content for the Web visitor. This makes the publisher happy, the reader happy and Google happy.
Google explains;
Section targeting allows you to suggest sections of your text and HTML content that you'd like us to emphasize or downplay when matching ads to your site's content. By providing us with your suggestions, you can assist us in improving your ad targeting.
The AdSense Support page has more information on "What is section targeting and how do I implement it?" JenSense has her views as well. And of course we have a thread on the topic at WebmasterWorld.
