Real-Time Bidding (RTB) is a digital advertising process where ad inventory is bought and sold on a per-impression basis via real-time auctions that occur within milliseconds. When a user visits a webpage, an auction is triggered in which advertisers bid for the opportunity to display their ads to that user. The highest bidder's ad is then shown almost instantly. RTB allows advertisers to target specific audiences and optimize their ad spend by bidding for impressions that are most valuable to them.