Prebid is an open-source collection of tools used in header bidding, a technique that helps publishers seek bids from multiple advertising demand sources before choosing how an ad impression will be sold. Its best-known component, Prebid.js, runs in the browser and coordinates requests to participating bidders.
In a common setup, Prebid collects responses from demand partners and passes information about those bids to the publisher's ad server. The ad server can then compare those opportunities with other eligible advertising demand. Prebid Server offers related server-side capabilities; the exact auction flow depends on the publisher's configuration.
Publishers use header bidding to reduce dependence on a single pathway for selling ads and to increase competitive pressure between buyers. Yet it is not a guarantee of higher revenue. Additional partners can increase complexity, latency and privacy-management obligations, and bidders may have different reporting and fee arrangements.
Prebid became particularly important in the Google advertising-technology antitrust remedies because interoperability with Google products can affect access to competing demand. When reading claims about integration, distinguish a court's requirement to support an interface from evidence that the integration has been completed or works well in practice.