How to add the EPEL repo to CentOS 7

What is EPEL repo?

Many online guides talk about the EPEL (or Extra Packages for Enterprise Linux) repository for CentOS.  It allows the easy installation of additional packages through yum.  These packages aren’t distributed as standard with RedHat Enterprise Linux or any of the downstream versions such a CentOS, Oracle or Scientific.  Additionally, it’s easy to keep them up to date through yum.

Although based on Fedora packages, the packages will never replace those which are standard in CentOS.

How can I install the repo?

[user@server] sudo yum install epel-release

I want to know more

There are more details on the official Fedora Project EPEL page.