Network Address Translation. A process that allows a network device like a firewall to assign one set of Inter Protocol (IP) addresses to computers within a private network, or local area network (LAN), and a second set of IP Addresses for external traffic. Inter-network traffic is remapped, converting an internal IP to one of the preassigned IP addresses specified for outgoing data. Companies use NAT to cut down on the number of IP addresses they need and to provide an extra layer of security.