proxy introduction

A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource, available from a different server.A proxy server may optionally alter the client's request or the server's response, and sometimes it may serve the request without contacting the specified server. In this case, it would 'cache' the first request to the remote server, so it could save the information for later, and make everything as fast as possible.The proxy server provides the resource by connecting to the specified server and requesting the service on behalf of the client
Gateway:
A proxy server that passes all requests and replies unmodified is usually called a gateway.