# firewall

Pronunciation: US say "FY-er-wawl" /ˈfaɪ(ə)ɹˌwɔl/; UK say "FY-uh-wawl" /ˈfaɪə.wɔəl/

## Noun

1. Software that monitors traffic entering and leaving a private network or personal computer, allowing or blocking it based on its perceived threat.
   - Simple: A security program that checks data coming into and out of a computer and blocks anything unsafe.
   - _The company installed a firewall to keep intruders out of its internal network._
   - _When the firewall flagged the incoming packets, the administrator reviewed the logs._
2. A fireproof barrier that prevents the spread of fire between or through buildings, vehicles, or aircraft.
   - Simple: A wall built to stop fire from spreading from one part of a building to another.
   - _The firewall in the engine compartment shields the cabin from heat and flames._
   - _Each townhouse is separated from the next by a firewall rated for two hours._
6. A hypothetical region of high-energy quanta that an observer falling into a black hole would encounter at or near the event horizon.
   - Simple: A possible wall of high-energy particles that anything falling into a black hole would hit at its edge.
   - _Whether a firewall forms at the event horizon remains a matter of theoretical debate._
   - _A firewall would violate the equivalence principle by making the horizon a special place._

## Verb

3. To protect a computer or network by installing and configuring a firewall.
   - Simple: To protect a computer or network by using a firewall.
   - _The administrator firewalled the entire subnet to limit outside access._
   - _They firewall every new server before it goes live._
4. To block specific traffic, an address, or a connection by means of a firewall.
   - Simple: To stop certain data or connections from getting through by using a firewall.
   - _The IT department firewalled the malicious IP range within minutes._
   - _Network admins firewall any port that isn't actively in use._
5. To run an engine or vehicle at maximum power or acceleration. *(slang)*
   - Simple: To push an engine to full power so a vehicle speeds up as fast as it can.
   - _Racers firewall through the final lap, engines screaming._
   - _He firewalled as soon as the track straightened out._

## Origin

Formed from 'fire' plus 'wall', with cognates in related languages such as Dutch brandmuur and German Brandmauer. The verb meaning of using maximum power or acceleration comes from the engine's firewall marking the limit of the throttle's forward movement, so to get full engine output one would push the throttle all the way to the firewall.

Source: DictionaryAI, https://dictionaryai.com/define/firewall (written from Wiktionary data, CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/).