What is a firewall?

A firewall is best defined as a network security device that monitors and controls incoming and outgoing network traffic based on predetermined security rules. This definition highlights the primary function of a firewall: to serve as a barrier between a trusted internal network and untrusted external networks, such as the internet. By applying specific rules, it can allow or deny traffic to maintain security and protect sensitive data from unauthorized access.

Firewalls operate by inspecting data packets traveling between networks and making decisions based on the configured rules, which can include criteria such as IP addresses, ports, and protocols. They can be implemented in both hardware and software forms, providing flexible options for securing both individual devices and entire networks.

The other options do not capture the essence of what a firewall is and how it functions. A software for data backup solutions focuses on data recovery rather than security. A type of network cable pertains to the physical medium for connectivity, with no direct relation to security practices. An algorithm for data compression relates to data storage efficiency but does not involve the security monitoring and control that defines a firewall.