Third-party cookie

Third-party Cookies do not come from the actively visited website itself, but are generated by third parties advertising on the website. The data collected by advertisers is not personally identifiable per se, but may provide information about user demographic, browser version, device, etc. and may be linked to personal information through click path tracking.

More about Third-Party Cookie and Data on Piwik PRO Blog:

First-Party vs Third-Party Cookies: Why First-Party Is the Way to Go