What is a firewall, and what is the difference between a network firewall and a host-based firewall?

A firewall controls traffic to prevent unauthorized access; a network firewall sits between two or more networks, while a host-based (personal) firewall is installed on an individual end system.

A firewall is one of the most effective security tools for protecting users from external threats by controlling what traffic is permitted or denied.

• Network firewall - Resides between two or more networks, controls the traffic between them, and helps prevent unauthorized access.
• Host-based (personal) firewall - Installed directly on an end system to protect that individual host.

Firewalls complement, rather than replace, each other — a network firewall guards the perimeter while host-based firewalls protect endpoints even on the internal network.

Go deeper:

• What is a Firewall? — PowerCert Animated Videos — contrasts host-based (software) and network-based firewalls with animation.
• Firewall (computing) — Wikipedia — host-based vs network firewalls and how they layer together.