What is NAT loopback?

This article demonstrates what is NAT loopback. It's useful when you run the server inside the network. After properly configuring the open port, port redirection or DMZ host, you can use the public IP address (or domain name) to access the server from both your home or office network as well as from the Internet.

The internal Web server shown in the image below, which can be accessed by the user in the local network using the public IP(1.2.3.4) or domain name(example.com).