Final answer:
A firewall is a device that blocks undesirable traffic between networks and enhances network security.
Step-by-step explanation:
A firewall is a device usually installed between two or more networks to block undesirable traffic. It acts as a barrier or filter, allowing only authorized traffic to pass through and restricting access to unauthorized or malicious content. Firewalls can be hardware-based or software-based and are a fundamental component of network security.