Digital Lexicon Hub

An auction process in which individual digital ad impressions are offered and bid on in near real time.

RTB lets advertisers decide what to pay for each individual impression based on context and audience, instead of buying fixed blocks of inventory, and lets publishers capture competitive prices for each ad slot.

When a page loads, an SSP sends a bid request with the URL, ad size and device; a DSP checks targeting rules, predicts a 0.4% click rate, returns a $6 CPM bid within 100 ms, and the highest valid bid serves its creative.

Every auction exposes some user data through bid requests, which raises privacy and consent obligations. Speed limits leave little room for complex decisions, and auction mechanics such as first-price bidding can lead to overpaying without bid shading.

A publisher's ad server or SSP sends a bid request, usually in OpenRTB JSON or Protobuf, to exchanges and DSPs. Bidders must answer within a timeout set by the tmax field, typically between 80 and 1,000 ms. Most exchanges now run first-price auctions, after which the winning DSP is notified, its creative renders and the impression is billed.