Google Ads Data Hub (ADH) is Google's data clean room environment, which was developed as a privacy-safe replacement for DoubleClick. 

This enabled brands to access impression-level data across all of their media campaigns in Campaign Manager, Display & Video 360 (DV360), Google Ads, and YouTube Reserve.

As cookies go away and Google sunsets its Data Transfer Files, which many advertisers have relied on to get access to raw event-level data that includes UserIDs, Google ADH will be the only environment with access to this granular level of information.