Glossaryprogrammatic advertisingpublisher metrics

Fill Rate

fill ratead impressionsinventorypublisherperformance metricsad space utilization

The percentage of a publisher's available ad inventory that is actually sold and filled with ads over a given period.

Formula: Fill rate = ad impressions generated in the ad space ÷ total inventory available on that ad space

Fill rate is a key metric for publishers tracking how effectively their inventory is being monetized. A fill rate of 100% would mean every available ad slot was served an ad; in practice, rates are typically lower due to unfilled or unsold impressions. Publishers use this metric to identify gaps in demand coverage and optimize their monetization strategy across direct deals, programmatic channels, and header bidding setups.

Waterfalling
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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…
Ads.txt
A text file that publishers place on their web server, configured by site administrators, that acts as a whitelist of authorized selling partners. It specifies exactly which supply-side platforms (SSPs) and ad exchanges…
Supply-Side Platform (SSP)
An advertising-technology platform used by publishers to sell ad inventory in an automated fashion, typically through Real-time bidding (RTB) auctions. SSPs are most commonly used by online publishers — websites and…