Proxy server is a computer that sits between a client computer and a real server, and provides indirect network services to a client. A proxy server intercepts all client requests, and provides responses from its cache or forward the request to the real server. Proxy servers are used for a few purposes. If it is used as a caching web proxy, it can dramatically improve performance of a web response. When a request is made by a client, a caching proxy returns response directly from its cache if the document exists. Otherwise, it makes the request to the real server, returns the result, and save it in its cache for later use. Proxy servers may also be used as a web proxy to filter web page contents. An organization or company may use a proxy server to block offensive web contents from viewed by the users. Internet Service providers may also use proxies to block computer viruses and other offensive contents.

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In computer networks, a proxy server is a server (a computer system or an application program) that acts as an intermediary for requests from clients seeking resources from other servers. 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. The proxy server evaluates the request according to its filtering rules. For example, it may filter traffic by IP address or protocol. If the request is validated by the filter, the proxy provides the resource by connecting to the relevant server and requesting the service on behalf of the client. 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 'caches' responses from the remote server, and returns subsequent requests for the same content directly.

A proxy server has a large variety of potential purposes, including ...more

In computer networks, a proxy server is a server (a computer system or an application program) that acts as an intermediary for requests from clients seeking resources from other servers. 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. The proxy server evaluates the request according to its filtering rules.

A proxy server is a server that acts as an intermediary for requests from clients seeking resources from other servers. 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. The proxy server evaluates the request according to its filtering rules. For example, it may filter traffic by IP address or protocol. If the request is validated by the filter, the proxy provides the resource by connecting to the relevant server and requesting the service on behalf of the client. 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 'caches' responses from the remote server, and returns subsequent requests for the same content directly.
sources
http://en.wikipedia.org/wiki/Proxy_server