"firewalls" in the noun sense
colloquial) the application of maximum thrust
"he moved the throttle to the firewall"
computing) a security system consisting of a combination of hardware and software that limits the exposure of a computer or computer network to attack from crackers commonly used on local area networks that are connected to the internet
a fireproof (or fire-resistant) wall designed to prevent the spread of fire through a building or a vehicle
Source: WordNet® (An amazing lexical database of English)
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