The system UUID is a unique identifier used in the inventory subscription service. This UUID can be used to re-register the system if there is some kind of corruption or for internal tracking.
From the command-line, use the identity command to return the current UUID. The UUID is the Current identity is value.
[root@server1 ~]# subscription-manager identity Current identity is: 63701087-f625-4519-8ab2-633bb50cb261 name: server1.example.com org name: 6340056 org id: 8a85f981302cbaf201302d89931e059a