See Application Proxy Firewall

A host computer that runs the Oracle Net Firewall Proxy. An application gateway looks and acts like a real server from the client's point of view, and a real client from the server's point of view. An application gateway sits between the Internet and company's internal network and provides middleman services (or proxy services) to users on either side.

n. Software running on a machine that is intended to maintain security on a secluded network yet allow certain traffic to go between the private network and the outside world. See also firewall.