Programmatic
Ad request
An ad request is the signal a web page, app or video player sends to an ad server or ad platform asking for an ad to fill a specific slot.
An ad request is the first step in delivering an ad. When a page loads (or a user scrolls to a slot, or a video reaches an ad break), code on the page or in the app asks: "I have a space here; send me an ad." That request carries information such as the ad unit, size, page URL or app bundle, device and consent signals.
The request may go directly to a publisher ad server, or first through header bidding or an app's ad mediation layer. Each request can then spawn many bid requests to buyers. Ad requests are the denominator of fill rate: requests that get an ad back are "filled".
The terms blur. Ad call is often used interchangeably; some teams use "ad request" for the page's request and "ad call" for the ad server's outgoing call to a creative or partner. Sudden surges in ad requests, especially with low fill and zero engagement, are a common sign of bot traffic or auto-refresh abuse.
Think of it like this
An ad request is like a customer raising a hand in a restaurant: it signals that a table is ready to be served, but no dish has arrived yet.
An example
A single mobile article page with four slots sends four ad requests on load and two more when the user scrolls, for six in total.
Related terms
Ad call
An ad call is the HTTP request an ad tag makes asking an ad server or partner to return an ad; it is often a synonym for ad request.
Fill rate
Fill rate is the percentage of ad requests that are actually filled with an ad, calculated as impressions served divided by ad requests, multiplied by 100.
Bid request
A bid request is the message an SSP or exchange sends to potential buyers describing an available ad impression, inviting them to bid on it in a real-time auction.
Ad slot (ad unit)
An ad slot (or ad unit) is a specific, defined place on a page, app screen or video stream where an ad can be shown, with its own size, format and rules.
Publisher ad server
A publisher ad server is the system a website, app or streamer uses to manage its ad inventory and decide, for every ad slot, which campaign or programmatic buyer gets the impression.