Application gateway
Alternatively referred to as an application firewall or application proxy, an application gateway is an application that is run on a firewall or proxy that negotiates a connection between a network application running on a computer behind the firewall and another computer. This connection provides added security to computers behind the firewall by only displaying the IP address of the firewall or proxy but at the cost of decreasing the overall speed you send and receive information.
Also see: Firewall, Network definitions, Proxy, Security definitions