firewall

Concise Oxford English Dictionary © 2008 Oxford University Press:
firewall/ˈfʌɪəwɔːl/

▶noun

• 1 a wall or partition designed to inhibit or prevent the spread of fire.

• 2 a part of a computer system or network which is designed to block unauthorized access while permitting outward communication.

▶verb Computing protect (a network or system) from unauthorized access with a firewall.