Google Adsense Tip #1: What is section targeting and how do I implement it?

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. We recommend that only those familiar with HTML attempt to implement section targeting.

To implement section targeting, you'll need to add a set of special HTML comment tags to your code. These tags will mark the beginning and end of whichever section(s) you'd like to emphasize or de-emphasize for ad targeting.

The HTML tags to emphasize a page section take the following format:

You can also designate sections you'd like to have ignored by adding a (weight=ignore) to the starting tag:With these tags added to your HTML code, your final code may look like the following:

Section targeting This is the text of your web page. Most of your content resides here.You can use section targeting to make suggestions about as many sections of a page as you like. However, please be aware that we can't guarantee results, and that it may take up to 2 weeks before our crawlers take into account any changes you've made to your site.

In order to properly implement this feature, you'll need to include a significant amount of content within the section targeting tags. Including insufficient content may result in less relevant ads or PSAs. In addition, please keep in mind that this feature should only be used to emphasize significant sections of your site's relevant content. It is against our program policies to manipulate the ad targeting to result in ads that are not relevant to the content of your pages.

Quoted from https://google.com/adsense/support/bin/answer.py?answer=23168.