What does Channels mean ?
Google Adsense Channels is one of many features Adsense offers, with channels you will be able to track each ad unit and how many page impressions it's got, Clicks it received, Click through rate '' CTR''
http://makemoneyonlineteacher.com/2009/11/20/what-are-google-adsense-channels-and-how-to-use-them/