firewall
a filter that decides which network traffic is let through
A firewall checks each piece of network traffic against a list of rules and lets it pass or blocks it. Rules can say which addresses, ports or services are allowed. Firewalls often sit on the router itself, between a business's network and the internet. Blocking a service at the firewall means outsiders cannot reach it at all.
Think of it as
Like a gatekeeper with a guest list who turns away anyone not on it.
Ideas that use this term