A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. Either hardware, software, or a combination of both, the firewall establishes a barrier between a trusted internal network and untrusted external networks such as the Internet. Its job is to permit legitimate outward communications while blocking unauthorized access, in order to keep hackers and viruses from reaching a single computer or a network of devices.

A web application firewall (WAF) is a network defense that filters, monitors, and blocks HTTP traffic to and from a web application. Unlike a regular firewall that serves as a safety gate between servers, a WAF is able to watch application-level traffic and decide to allow or disallow based on the data that is visible over the network.

In essence, firewalls act as a network security filtering system between the network and outside connections, monitoring and controlling incoming and outgoing communications to keep the enterprise safe.