Data from a variety of online and offline sources is used to target ads through real-time bidding (RTB). This data informs the bids buyers submit for each ad impression. More detailed data on users leads to higher bids. However, concerns remain about issues like viewability, fraud, and the large cut of spending that bypass publishers. Overall, while data targeting aims to improve efficiency and relevance, the complex RTB ecosystem still faces challenges around transparency, pricing, and metrics.