1) An ad which is served to a user’s browser. Ads can be requested by the user’s browser (referred to as pulled ads) or they can be pushed, such as e-mailed ads; 2) a measurement of responses by an ad delivery system to an ad request from the user’s browser, which is filtered from robotic activity and is recorded at a point as late as possible in the process of delivery of the creative material to the user’s browser — therefore closest to the actual opportunity to see by the user. Two methods are used to deliver ad content to the user – a) server-initiated and b) client-initiated. Server-initiated ad counting uses the Online Publisher’s Web content server for making requests, formatting and re-directing content. Client-initiated ad counting relies on the user’s browser to perform these activities. (See www.iab.net for details concerning ad campaign, broadband Video and Rich Media measurement guidelines).