What is the primary purpose of a 'firewall'?

The primary purpose of a firewall is to filter incoming and outgoing network traffic for security. A firewall acts as a barrier between a trusted internal network and untrusted external networks, monitoring and controlling the data packets that enter or leave the network. This capability is crucial for protecting systems from unauthorized access, data breaches, and malware. By implementing various security rules, a firewall can deny or allow traffic based on criteria such as IP addresses, protocols, and port numbers.

This function is vital for maintaining the integrity and confidentiality of an organization's data, making it a cornerstone of network security strategies. In contrast, other options like enhancing system performance, storing data securely, or optimizing internet speed do not accurately represent the core functionality and objective of a firewall.