Over the page (OTP) is an ad unit format which is served over the publisher webpage and is displayed for about 5 or 10 seconds. After that, the initial ad disappears and is replaced on the webpage by a more traditionnal ad unit.
Over the page format is intended for grabing attention and have high visual impact but is intrusive. For reducing intrusiveness, over the page ads are usually capped at one impression per day per visitor.
Over the page ads have higher click rates, but some clicks might be unintentional.
Yahoo Australia offer different OTP ad formats:
Image source: GourmetAds