Servidor especial encargado, entre otras cosas, de centralizar el tráfico entre Internet y una red privada, de forma que evita que cada una de las máquinas de la red interior tenga que disponer necesariamente de una conexión directa a la red. Al mismo tiempo contiene mecanismos de seguridad (firewall o cortafuegos) que impiden accesos no autorizados desde el exterior hacia la red privada.

A computer and associated software which will pass on a request for a URL from a World-Wide Web browser such as Mosaic to an outside server and return the results. This provides clients that are sealed off from the Internet a trusted agent that can access the Internet on their behalf. Once the client is properly configured, its user should not be aware of the proxy gateway. A proxy gateway often runs on a firewall machine. Its main purpose is to act as a barrier to the threat of crackers. It may also be used to hide the IP addresses of the computers inside the firewall from the Internet if they do not use official registered network numbers.