Firewall

A device that forms a barrier between a secure and an open environment. Usually the open environment is considered hostile. The most notable open system s the Internet. A network device used to filter traffic. A firewall is typically deployed between a private network and a link to the Internet, but it can be deployed between departments within an organization. Firewalls filter traffic based on a defined set of rules. System designed to defend against unauthorized access to or from a private network.