google_ad_section_start is a keyword that the Google Adsense service uses to focus on a page section. Or, more precisely, a webmaster of a web uses this keyword in the HTML code to emphasize a page section that he wants the Google crawlers to see and pay more attention to. This is called Google Ad Section.
Section targeting allows the webmaster to suggest sections of a page that should be emphasized by the Google AdSense, but it also allows the webmaster to downplay other sections when matching ads to the website's content.
Why google_ad_section_start is used
One of the largest problems with Google AdSense is that the ads that show at a website are often irrelevant to the content.
Having the inclusion/exclusion code helps Google AdSense to recognize what is important at the website (which in turn affects your ad-to-content matching which determines to a great degree your earnings in case you make money with AdSense). This is especially true of blogs where the ads might be about blogging, or related to menu items and not about the specific topic on that page.
The more relevant an ad is to the topic shown at a webpage, the higher the relevancy to the visitor reader, and the higher potential for revenue from ads.
How it is done
To implement section targeting, a set of special HTML comment tags (google_ad_section_start, google_ad_section_end) needs to be added into the website code. These tags will mark the beginning and end of whichever section(s) that should be emphasized or de-emphasized for ad targeting.
Google ad section Syntax
The HTML tags to emphasize a page section have the following format:
<!-- google_ad_section_start -->
Important text that should be emphasized for Google Adsense.
<!-- google_ad_section_end -->
<!-- google_ad_section_start(weight=ignore) -->
Text that should be de-emphasized for Google AdSense.
<!-- google_ad_section_end(weight=ignore) -->
Can I have more than one Google ad section at my website?
You can use section targeting to make suggestions about as many sections of a page as you like.
How long does it take for the change to take effect?After you add the google_ad_section_start, google_ad_section_end tags to your HTML code, it can take as long as two weeks for the Google Adsense crawlers to take the code on your pages into account.
What happens if this code does not work?
If for example you make a typo in this code, your website should not get skipped by Google. This code is not a command, it works more as a "suggestor". If it is wrong, then Google does not see it. And because it is in the HTML comment format, a browser does not display it to the user either.
It can happen that you include the start weight=ignore tag and forget to close it. In this case, you would find out about the mistake by having either ads unrelated to your content at your website or by showing public service ads.
Note, you will see public service ads at your website also if you do not include enough content in the section that is supposed to be included.
What is forbidden?
This inclusion/exclusion feature should only be used to emphasize significant sections of a page. It is against Google's policies to manipulate the ad targeting to result in ads that are not relevant to the content of your pages.
Questions about Google ad section
You might be interested in the following articles which relate to Google advertising:
In case you have any questions about anything related to building websites or SEO, you are welcome to ask questions in our SEO discussion forum. Here is a thread specifically related to google_ad_section.