Storage Partitioning
Also known as: state partitioning, total cookie protection
Keeping cookies, cache and storage separated per top-level site so trackers can't correlate across the web.
Traditionally, a third-party script (an ad, a widget) shared one global storage bucket across every site it was embedded on — the foundation of cross-site tracking. Storage partitioning gives each top-level site its own isolated jar for every third party it loads.
Safari's ITP, Firefox's Total Cookie Protection and Chrome's storage partitioning all implement variants of this idea. It's arguably the most impactful anti-tracking change of the last decade.