Apple’s press release:
Safari can automatically use Reader to open articles in a clean, uncluttered format, while Autoplay Blocking stops media with audio from automatically playing in the browser.
Intelligent Tracking Prevention in Safari uses machine learning to identify and remove the tracking data that advertisers employ to follow users’ web activity.
It wasn’t mentioned in the keynote, but iOS 11 also includes Intelligent Tracking Prevention. These two enhancements alone are enough reason to try to explain to friends and family what High Sierra is and why they should update once it’s out. Good luck getting anyone used to that name, though.