Demilitarized Zone (DMZ) is an area between two networks, that is accessible from both networks. This is generally where public servers are located. VLANs and Subnets can provide a similar function within a network, but not between two separate networks.
In computer security, a DMZ or demilitarized zone (sometimes referred to as a perimeter network or screened subnet) is a physical or logical subnetwork that contains and exposes an organization's external-facing services to an untrusted, usually larger, network such as the Internet. The purpose of a DMZ is to add an additional layer of security to an organization's local area network (LAN): an external network node can access only what is exposed in the DMZ, while the rest of the organization's network is firewalled. The DMZ functions as a small, isolated network positioned between the Internet and the private network.The name is from the term demilitarized zone, an area between states in which military operations are not permitted.