[CentOS] nsswitch.conf question

Mon Jan 11 20:44:37 UTC 2016
Nicholas Geovanis <nickgeovanis at gmail.com>

I find the passwd, shadow and group lines in my CentOS 7 /etc/nsswitch.conf
file specify "files sss". I'm not familiar with the "sss" source, would
someone please give me an idea what that is? Many thanks....Nick