What is the primary function of a firewall?

A firewall is a network security system that monitors, filters, and controls incoming and outgoing network traffic based on predefined security rules. Its primary purpose is to prevent unauthorized access while allowing legitimate communication between trusted and untrusted networks, such as the Internet. Firewalls protect computers and networks from cyber threats, including hackers, malware, and unauthorized users, and can be implemented as hardware, software, or a combination of both.