Google AdSense is introducing expandable ads to their ad offering. Expandable ads are ones that increase when an action is taken. With some networks, ads increase in size when a user mouses over or scrolls a page. But AdSense's expandable ads will increase only when clicked on.
The AdSense expandable ads will only increase up to double the width or height of the original display. Users can click to close the ad at any time. The ads can include rich media such as video and images.
Advertisers will pay based on a cost-per-click (CPC) or cost-per-impression (CPM) basis. CPC ads will only cost the advertiser when users click through to the landing page.