https://www.vice.com/en_us/article/5dmgkz/what-are-third-party-internet-cookies-and-why-is-google-killing-them

Google this week announced that the company will take steps to eventually eliminate third-party cookies, routinely used by data brokers to closely track and profit from your browsing behavior. But experts say that while the company’s announcement is a good first step, the effort is belated, murky, and not quite the revolution it’s being portrayed as. In a blog post, Justin Schuh, Director of Chrome Engineering, announced that the company’s Chrome browser would be moving away from using third-party cookies sometime in the next two years. First party cookies would still be allowed, but third party cookies used to track you around the internet would eventually be banned.

First party cookies are doled out by the sites you visit directly, retaining login information, site settings, and other details. Third party cookies, in contrast, are created by web domains other than the one you’re currently visiting; they’re predominantly used to track your browsing activity across websites, retargeting, and ad delivery.