Responsive Creative on Google specifically relates to the combination and formatting of the ads themselves.

In Performance Max and Demand Gen, we provide different pieces of the Ad, but the machine learning system mixes and matches to put the ad together. This leverages Google’s Machine Learning in a really interesting way. Instead of us having to test different ad sets, the Machine learning mixes and matches and learns – working to determine the optimal combination of assets for each ad slot based on the performance history and patterns of the user themselves.