How to enable ELRepo repository on CentOS or RHEL

While CentOS/RHEL platforms maintain several official repositories (e.g., base, updates, contrib), they are lacking in terms of software coverage and release cycles. To bridge the gap between what is available and what is commonly needed, third-party repositories are created to serve community needs for commonly requested software packages. One such third-party software repository for CentOS/RHEL is ELRepo (The Community Enterprise Linux Repository).