Red Hat Enterprise Linux commonly but not officially abbreviated as RHEL is a Linux distribution developed from commercial point of view. Red Hat Enterprise Linux provides their source code for free but keep check on free re-distribution of their officially supported version of Red Hat Enterprise Linux. All the third party derivatives and community supported distributions be it CentOS, Oracle Linux and Scientific Linux build and redistribute their distribution by removing non-free components and Trade mark of Red Hat.
http://www.tecmint.com/redhat-enterprise-linux-7-1-installation/
