Final answer:
A firewall is a network security device that acts as a barrier between a trusted internal network and an untrusted external network. It monitors and filters incoming and outgoing network traffic to prevent unauthorized access and protect sensitive data.
Step-by-step explanation:
A firewall is a network security device that monitors and filters incoming and outgoing network traffic based on predetermined security rules. It acts as a barrier between a trusted internal network and an untrusted external network, such as the internet.
Firewalls analyze incoming and outgoing traffic to determine whether it should be allowed or blocked based on criteria set by the network administrator. They can prevent unauthorized access to a network, protect sensitive data, and help mitigate the risk of attacks.
For example, if a hacker attempts to gain access to a network by sending malicious traffic, a firewall can block that traffic and prevent the hacker from entering the network.