A Network Firewall is a security device that monitors and controls incoming and outgoing network traffic based on predetermined security rules. It acts as a barrier between a trusted internal network and untrusted external networks, such as the Internet. By filtering traffic, it helps protect systems from unauthorized access and cyber threats. Firewalls can be hardware-based, software-based, or a combination of both. They can also provide features like VPN support, intrusion detection, and logging of network activity. Overall, a network firewall is essential for maintaining the security and integrity of a network.