Channels enable you to view detailed reporting about the performance of specific pages and ad units. By assigning a channel to a combination of pages or ad units, you could track the performance of a leaderboard versus a banner, or compare your motorcycle pages to your automobile pages. You can even create a channel to track each of your separate domains, so you can see where your clicks are coming from. While channels can be used to track performance and revenue, they won't have any effect on your earnings or ad targeting.
There are two types of channels from which to choose: URL channels, and custom channels.
URL Channels
Use URL Channels to track your performance without modifying your ad code. By entering a full or partial URL, you can begin tracking the performance of particular pages in your site. You can enter a top-level domain name to track all of the pages on that domain, or you can enter a partial URL to track all of the pages below a certain directory. Entering a full URL will track the performance of that particular page.
URL channels are only available for AdSense for content pages. If you would like to track your AdSense for search performance, please use custom channels.
Custom Channels
Custom channels allow you to track the performance of specific ad units based on your specified criteria. By pasting channel-specific ad code into your pages, you can track a variety of metrics across a range of URLs. Use custom channels to track the performance of different ad formats, for example, or to compare different page topics to one another.
You can also turn any custom channel into an ad placement on which advertisers can choose to place their ads.
With up to 200 AdSense channels, plus 200 AdSense for search channels available for each publisher, you can use channels to gain the insight you need to optimize your site's performance. It's easy to add, deactivate, or rename your channels, and customized reports are simple to generate.