The process of purchasing and selling digital ad space through real-time auctions that occur in the time it takes a webpage to load.
In Real-time bidding (RTB) auctions, advertisers (via Demand-side platform (DSP)s) bid on individual impressions put forward from publishers (via Supply-side platform (SSP)s and Ad exchanges).
The whole bidding process is super fast, usually taking less than 200 milliseconds. For perspective, it takes about 300 milliseconds to blink!