Google’s expanding on the recent addition of custom channels in AdSense and is now allowing publishers to create premium inventory on their site with the use of new “ad placements”.
Think of ad placements as ‘enhanced’ custom channels. To create an ad placement, you create and implement a custom channel just as you normally would. The only change is the additional step of providing attributes and an accurate description for your ad placement. On the ‘Channels’ page in your account, click the appropriate ‘edit settings’ link on the right. As you can see below, there will be a box labeled ‘Targeting’ on the next page which, once checked, will show this channel to advertisers as an ad placement.
AdSense publishers then describe where each ad placement is located on their site, so advertisers can target their ads. Here’s how it looks: