Repository is a way to install packages in Linux. The Extra Packages for Enterprise Linux (EPEL) repository provides extra software packages that are not included in the official CentOS or Red Hat Enterprise Linux repositories.
CentOS5.x or RHEL5.x
rpm -ivh epel-release-5-4.noarch.rpm
CentOS6.x or RHEL6.x
rpm -ivh epel-release-6-8.noarch.rpm
CentOS7.x and Red Hat 7.x
rpm -ivh epel-release-7-2.noarch.rpm
Note: This artical written in Nov5, 2014. Might be newver version is avaible in future. This is recommended to visit https://fedoraproject.org/wiki/EPEL if you get file not found message.