Firewall 

Firewall

A Firewall is a set of related programs, located at a network gateway server that protects the resources of a private network from users from other networks. Basically, a firewall, working closely with a router program, filters all network packets to determine whether to forward them toward their destination. A firewall is often installed away from the rest of the network so that no incoming request can get directly at private network resources. There are a number of firewall screening methods. A simple one is to screen requests to make sure they come from acceptable (previously identified) domain names and IP addresses. For mobile users, firewalls allow remote access in to the private network by the use of secure logon procedures and authentication certificates.
A combination hardware and software buffer that many companies or organizations have in place between their internal networks and the Internet. A firewall allows only specific kinds of messages from the Internet to flow in and out of the internal network. This protects the internal network from intruders or hackers who might try to use the Internet to break into those systems.
A combination of hardware and software that secures access to and from the LAN. There are three main types of firewall architecture; Tasteful Inspection, Proxy based and Packet Filtering, whereby the former provides the highest level of access control. Firewalls can also be used to secure internal network resources from internal network users too.
A fortress between networked computers within an organization and those outside the organization. It is commonly used to protect information such as a network's e-mail and data files within a physical building or organization site. The area within the firewall is called the demilitarized zone, or DMZ. Often, a single machine in the DMZ is allowed access to both internal and external computers. The computer in the DMZ is directly interacting with the Internet, so strict security measures on it are required.
A system or combination of systems that enforces a boundary between two or more networks. Gateway that limits accesses between networks in accordance with local security policy. A system designed to protect a computer network from unauthorized access, especially via the Internet. Both the House and Senate maintain strong firewalls to ensure that congressional data -- both on and off the Internet -- remains safe.