AdSense channels are designed to help you find out where AdSense is earning you the most money. The AdSense channels give you a deeper level of reporting than the standard AdSense revenue reporting. The following information is tracked for each channel:
Impressions
CTR (Click Through Rate)
CPM (Cost Per Thousand Impressions)
Earning Statistics for a particular channel
There are two kinds of channels: URL Channels and Custom Channels. URL Channels are for domains, subdomains, and page-specific reporting. With a URL channel, you can learn which of your URLs, pages, or resources are earning the most money. Custom channels, on the other hand, are designed for much finer detail, including ad placement or a particular ad unit.
Creating a URL channel is easy. After you log in to your AdSense account, click the Channels link, type a name for your channel, and click OK.
To create a Custom Channel, click the AdSense Setup tab, click the Channels link, and then click Add new custom channel.