Intelligent Tracking Prevention (ITP)

ITP is a feature developed by WebKit, an engine used in Safari and other browsers, that reduces cross-site tracking by further limiting cookies and other website data.

It was designed to recognize and then prevent domains with tracking capabilities from following users across the web using first-party cookies.
Read more about ITP on Piwik PRO blog:
What Intelligent Tracking Prevention (ITP) 2.1 means for web analytics & marketing