Final answer:
A firewall is a crucial network security device that protects a user's computer from unauthorized access by inspecting and controlling incoming and outgoing traffic based on defined rules.
Explanation:
Firewall is a network security device that acts as a barrier between a user's computer and the network/internet to block unauthorized access. It inspects incoming and outgoing traffic and applies defined rules to allow or deny packets, preventing unauthorized access and data theft. Firewalls can be software or hardware, providing essential protection against cyber threats.
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