The new guidelines are voluntary and aim to make interactive advertising easier to buy. They follow a six-month study conducted by PricewaterhouseCoopers into the problems of measuring ad impressions.
The new guidelines identify and define five key metrics in the measurement process - ad impressions, clicks, visits, "unique" measurements (browsers, visitors and users), and page impressions. They point to site-side data disclosure as being integral to accurate measurement and reporting of interactive advertising data.
The guidelines and PwC study are available on the IAB's site. Registration is required to download them.