Glossaryprogrammatic advertisingad serving

Ad Slot

ad slotad tagad servercreative deliverypublisherad placement

An ad slot is the physical space on a webpage where ads appear. Publishers place ad slots in strategic locations across their site — typically areas where ad visibility and engagement are highest.

Each ad slot contains an ad tag, a small snippet of code that communicates with an ad server to determine which creative (ad format) gets served into that space. The ad tag effectively acts as the bridge between the publisher's page and the ad-serving infrastructure, triggering the process that selects and loads the appropriate ad.

Ad slot visualisation

Ad Call
Also known as: ad request An ad call is a request sent from an ad slot on a web page or app to an AdTech platform — typically an ad exchange or ad server — for the purpose of serving an ad to the user. Ad calls usually…
Decisioning
The process by which AdTech platforms — including ad servers, supply-side platforms (SSPs), demand-side platforms (DSPs), and ad exchanges — determine which ad to serve for a given impression. The decision is driven by…
Daisy Chain
Also known as: waterfalling, the publisher's waterfall A daisy chain is a media-buying process in which a publisher's ad server loads ad network, SSP, and ad exchange tags sequentially — one after another — until an ad…
Ad Unit
Also known as: ad placement A single unit of ad space available on a publisher's website or mobile app. Ad units represent the discrete slots into which advertisers serve creative — a banner position at the top of a…