https://arstechnica.com/gadgets/2021/04/everybody-hates-floc-googles-tracking-plan-for-chrome-ads/

Google wants to kill third-party tracking cookies used for ads in Chrome with the "Chrome Privacy Sandbox." Since Google is also the world's largest ad company, though, it's not killing tracking cookies without putting something else in its place. Google's replacement plan is to have Chrome locally build an ad interest profile for you, via a system called "FLoC" (Federated Learning of Cohorts). Rather than having advertisers collect your browsing history to build an individual profile of you on their servers, Google wants to keep that data local, and have the browser to serve a list of your interests to advertisers whenever they ask via an API, so that you'll still get relevant ads. Google argues that conscripting the browser for ad interest tracking is a win for privacy, since it keeps your exact browsing history local and only serves up anonymized interest lists. Google does not have many other companies in its corner, though.