The main purpose of a firewall in cybersecurity is to protect a network by controlling incoming and outgoing traffic based on predetermined security rules. Firewalls serve as a barrier between trusted internal networks and untrusted external networks, such as the internet. They monitor and filter traffic to prevent unauthorized access, malware infections, and data breaches. Firewalls can be implemented as hardware devices or software applications and often include features like intrusion detection and prevention systems. Overall, firewalls are essential components of a comprehensive cybersecurity strategy, helping organizations safeguard their sensitive information and systems.