The first type of relationship between a website and an advertiser was a straightforward, direct partnership. This partnership model implies that the advertiser promoting a product or service pays the website (also known as a publisher) directly for a certain amount of ad impressions. As time went on, publishers began creating thousands of websites, leading to millions of pages with unsold ad space. This gave rise to a new set of companies called Ad Networks. The ad network acted as a broker, buying unsold ad space from multiple publishers and packaged them into audiences to be sold to advertisers. This second wave of advertiser-publisher relationships rapidly gained popularity as it was convenient and useful for buyers who often found themselves paying a lower price yet receiving enhanced targeting capabilities through ad networks.