AdSense spiders will crawl your site and search for content when "deciding" what ads to display on your site. Sometimes they can get confused by navigation content, footer content, other ads and other information on your site. AdSense offers a solution.
By using "Section Targeting," the spiders will locate only the content that you select to be targeted. Therefore, AdSense will place ads that are more relevant to your site's theme and content. Use the following HTML tags:
<!-- google_ad_section_start -->
<!-- google_ad_section_end -->
Designate sections to have ignored by adding a (weight=ignore) to the starting tag:
<!-- google_ad_section_start(weight=ignore) -->