A device that handles network traffic on behalf of another: a client will send a request to a proxy, which will then make the same request to a server, to which the proxy appears to be a client. The response from the server is returned to the proxy and then passed to the original client. Proxies are often used as part of a firewall to allow complex protocols to be handled; they may also examine requests and responses, route requests to different servers or filter responses in accordance with some policy.