Так называемый безопасный интернетовский шлюз" затрудняющий доступ злоумышленников к тому или иному серверу.

firewall
security system fitted to a server connected to the internet; if you connect your main office server to the internet to provide a WWW server, or if you connect your WWW server computer to the office server without a firewall, then any user on the internet could gain access to your office server by getting around the very basic WWW security functions. To stop hackers gaining access to your internal office network via an internet connection, you should fit a firewall. The firewall could be sophisticated software that checks the address of each user that tries to access your server and blocks any unknown users, or could be a hardware device that prevents sensitive information travelling between the office server and the WWW server. If you are connecting your desktop computer to the Internet using a modem, there is a very slight risk that someone could get into your computer whilst you are connected - but this does not warrant a firewall. If your office is permanently connected to the Internet (for example, to provide electronic mail) then there is more of a risk and you should install a firewall system

Установленное на маршрутизаторе (router) защитное средство, обеспечивающее фильтрацию поступающих в сеть сообщений.

Син. межсетевой экран

Happy New Year!

A firewall is a set of programs at a network gateway server, which serves as a logical discontinuity to prevent unauthorized access to data or resources. Another English term is “external firewall”, which is probably more descriptive. (In other words, a firewall is an authorization system that enforces a boundary between your company network and all the other users of the WWW.)

A firewall works with a router program. It will filter all network packets to see if they should be sent to their destinations, i.e. a firewall determines, if specific information should be provided at a given request. A firewall is also used with proxy servers (or will include one); this ensures that the firewall function is performed for all users of the workstation (usually, in an office with multiple users the firewall will be installed on one of the computers, which is called, internally, the “server”).

In terms of translation, the best Russian word for “firewall” is «брандмауэр», as suggested in all the answers above. I checked the term on the WWW for its Russian translation «брандмауэр», and found many results, which you may find useful, if more description of «брандмауэр» and other Russian-language terms is needed.

http://www.dvgu.ru/meteo/PC/brand.htm
http://www.webclub.ru/materials/sequritypolitics/isp6.html
http://security.nsys.by/articles/basics/isp6.htm
http://www.falc.newmail.ru/info/security_guide/glava6_1.htm

Regards.