Definition of "Firewall" :

noun: (colloquial) the application of maximum thrust

"He moved the throttle to the firewall."

noun: a fireproof (or fire-resistant) wall designed to prevent the spread of fire through a building or a vehicle

noun: (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