A firewall is a security system 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. Firewalls can be hardware-based, software-based, or a combination of both, and they help protect computers and networks from unauthorized access and cyber threats. Firewalls work by filtering data packets and determining whether to allow or block them based on specific criteria. They can also log traffic and alert users to potential security breaches. By using a firewall, individuals and organizations can enhance their cybersecurity and safeguard sensitive information from malicious attacks.