In computer networks, a proxy server is a server (a computer system or an application program) which services the requests of its clients by forwarding requests to 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 provides the resource by connecting to the specified 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 would 'cache' the first request to the remote server, so it could save the information for later, and make everything as fast as possible.
A proxy server that passes all requests and replies unmodified is usually called a gateway or sometimes tunneling proxy.
A proxy server can be placed in the user's local computer or at specific key points between the user and the destination servers or the Internet.
An anonymous proxy server (sometimes called a web proxy example is myspace proxy) generally attempts to anonymize web surfing. These can easily be overridden by site administrators, and thus rendered useless in some cases. There are different varieties of anonymizers.
Access control: Some proxy servers implement a logon requirement. In large organizations, authorized users must log on to gain access to the web. The organization can thereby track usage to individuals.
Many work places and schools restrict the web sites and online services that are made available in their buildings. Since circumventors are used to bypass censors in computers, social networking and other sites deemed a waste of time or resources have become targets of mass banning.
Proxy Web server creators have become more sophisticated, allowing users to encrypt links and any data going to and from other web servers. This allows users to access websites that would otherwise have been blocked.
A special case of web proxies are "CGI proxies". These are web sites that allow a user to access a site through them. They generally use PHP or CGI to implement the proxy functionality. These types of proxies are frequently used to gain access to web sites blocked by corporate or school proxies. Since they also hide the user's own IP address from the web sites they access through the proxy, they are sometimes also used to gain a degree of anonymity, called "Proxy Avoidance".