Firewall
Etymology
Literally a fire-resistant wall built to stop flames spreading between parts of a building or from a car’s engine into the cabin. Networking borrowed the image in the late 1980s for software that stops threats from spreading into a protected network. The metaphor is so vivid it now names any deliberate separation, as in a "firewall" between a newspaper’s business and editorial sides.
noun · /FYRE-wawl/
A barrier that filters network traffic, blocking unwanted or dangerous connections from getting through.
What it names
The guarded gate around a network — and, by extension, any protective boundary between a trusted inside and a hostile outside.
Example
The company firewall blocked the connection before the malware could phone home.
Related idea
A firewall controls which connections are allowed at the border, whereas encryption protects the contents of connections that do get through — you generally want both.
noun · /FYRE-wawl/
An enforced barrier that keeps two functions or parties separate to prevent a conflict of interest or the spread of trouble.
What it names
It generalizes the network sense to organizations — the wall between a bank's research and trading arms, or a newsroom and its advertisers — guarding against contagion of influence.
Example
A strict firewall separates the newspaper's editorial staff from its business side.
Related idea
It generalizes the network barrier to institutions — the wall guarding against a conflict of interest or the contagion of influence between a bank's research and trading arms.