Wikipedia
XKeyscore or XKEYSCORE (abbreviated as XKS) is a formerly secret computer system first used by the United States National Security Agency for searching and analyzing global Internet data, which it collects on a daily basis. The program has been shared with other spy agencies including the Australian Signals Directorate, Communications Security Establishment Canada, New Zealand's Government Communications Security Bureau, Britain's Government Communications Headquarters and the German Bundesnachrichtendienst.
The program's purpose was publicly revealed in July 2013 by Edward Snowden in The Sydney Morning Herald and O Globo newspapers. The codename was already public knowledge because it is mentioned in earlier articles, and like many other codenames can also be seen in job postings, and in the online resumes of employees.
On July 3, 2014 excerpts of XKeyscore's source code were first published by German public broadcaster Norddeutscher Rundfunk, a member of ARD. A team of experts analyzed the source code. Recent articles mention that XKEYSCORE uses user metrics to flag certain data, such as race, sex, ethnicity, and geolocation.