In computer networks, a DMZ (demilitarized zone), also sometimes known as a perimeter network or a screened subnetwork, is a physical or logical subnet that separates an internal local area network (LAN) from other untrusted networks -- usually the public internet. External-facing servers, resources and services are located in the DMZ. Therefore, they are accessible from the internet, but the rest of the internal LAN remains unreachable. This provides an additional layer of security to the LAN as it restricts a hacker's ability to directly access internal servers and data through the internet.
Any service provided to users on the public internet should be placed in the DMZ network. Some of the most common of these services include web servers and proxy servers, as well as servers for email, domain name system (DNS), File Transfer Protocol (FTP) and voice over IP (VoIP).