EPEL (Extra Packages for Enterprise Linux) is a volunteer-based community effort from the Fedora project to create a repository of high-quality add-on packages that complement the Fedora-based Red Hat Enterprise Linux (RHEL) and its compatible spinoffs, such as CentOS and Scientific Linux.
EPEL provide lots of packages for CentOS / RHEL, It is not part of RedHat or CentOS but is designed to work with these major distributions. Please note that EPEL only provides free and open source software unencumbered by patents or any legal issues. In short you will not find mp3, dvd and music / media player under EPEL. However, you will find many programs related to networking, monitoring, sys admin, programming and so on.
Packages are supplied in RPM format and in most cases are ready to use. Beware that some packages may break something and you should not blindly install those packages.
To enable EPEL for CentOS 5
# wget http://download.fedoraproject.org/pub/epel/5/i386/epel-release-5-4.noarch.rpm
# wget http://download.fedoraproject.org/pub/epel/5/x86_64/epel-release-5-4.noarch.rpm
To enable EPEL for CentOS 4For 32-bits
# wget http://download.fedora.redhat.com/pub/epel/4/i386/epel-release-4-10.noarch.rpm
# wget http://download.fedora.redhat.com/pub/epel/4/x86_64/epel-release-4-10.noarch.rpm