A multi-layer device that makes decisions on what data to forward on to it's destination, and what data to block from it's destination.
A filtering module located on a gateway machine that examines all incoming and outgoing traffic to determine if it may be routed to its destination. WinRoute provides an extensive firewall via: NAT's functionality, the assignment of rules for specified IP addresses, and the ability to record certain information going one way so it may be authorized on the way back.
Along with each IP address is a range of 65535 ports that an application may use. Web Servers, for example, use port 80. A firewall manages which ports to allow through, and more importantly which ones to block. A good firewall also can manage both incoming and outgoing connections to a port. So for example, it can allow outbound traffic on port 80, but deny incoming connections to port 80.