We're excited to introduce to you expandable ads, a new type of ad that can appear on your pages. Expandable ads are rich media ads that can
expand beyond the original size of the ad unit, following a
user-initiated action. This creates more real estate for the ad,
allowing for more interaction from interested users.
[...]
Expandable ads will be served
as third-party ads and will be created by Google-certified rich media
vendors for the top display advertisers in our network. And like other
Google ads, you'll earn based on whether the expandable ads on your
site are priced on a cost-per-click (CPC) or cost-per-impression (CPM)
basis. Keep in mind that you'll generate earnings from CPC expandable
ads when a user visits the advertiser's landing page, and not when a
user simply clicks to expand the ad.