GDN (Google Display Network) is a visual advertising network within Google's portfolio that includes websites, Youtube, and Gmail. In this network, visual ad spaces belonging to businesses are provided instantly through an auction process. The ad spaces are user-specific, meaning that, for example, ads won't be shown to all users on a specific news website throughout the day. Businesses target users based on interests, search terms, visited websites, and other criteria. If users within the target audience visit a website with visual ad spaces, or access Youtube or Gmail, the visual ads belonging to the business will be triggered. Source: https://www.efealtinelli.com/gdn-nedir-google-goruntulu-reklam-agi-rehberi/