What's a network segment for public-facing servers that's separated from a private, trusted network by a firewall?

What's a network segment for public-facing servers that's separated from a private, trusted network by a firewall?

• DMZ
• NSA
• VPN
• ATA 

EXPLANATION

A DMZ, or demilitarized zone, is a physical or logical subnetwork that contains and exposes an organization's external-facing services to a larger and untrusted network, usually the Internet. The purpose of a DMZ is to add an additional layer of security to an organization's local area network (LAN).

SOURCE

http://www.ciscopress.com/articles/article.asp?p=1823359