In your house, a firewall is a physical feature of the building made of fire resistant materials. It’s designed to slow the progress of fire and heat to protect the people and possessions behind the firewall. In a network, a firewall is a security feature designed to slow the progress of ne’er-do-wells that might try to access your network without your permission. A firewall can be a piece of software installed on your computer, or it could be a networking device that comes pre-loaded with security applications and purpose-built hardware designed to prevent unwanted network intrusions.