An ad exchange is a digital marketplace where advertisers and publishers come together to buy and sell online advertising space. It acts as a middleman, connecting advertisers looking to promote their products or services with publishers who have available ad space on their websites. Ad exchanges use real-time bidding technology to facilitate the buying and selling of ads, allowing for more efficient and targeted advertising. This platform allows for a more transparent and competitive market, giving advertisers the ability to reach their desired audience and publishers the opportunity to maximize their ad revenue. In essence, an ad exchange is a virtual hub for the buying and selling of online advertising, making it an essential tool for the ever-evolving world of digital marketing.