Web proxy

Proxies that focus on WWW traffic are called web proxies. Many web proxies attempt to block offensive web content. Other web proxies reformat web pages for a specific purpose or audience (e.g. cell phones and PDAs or persons with disabilities)

Many organizations — including schools, corporations, and countries — use proxy servers to enforce acceptable network use policies (see content-control software) or to provide security, anti-malware and/or caching services. A traditional web proxy is not transparent to the client application, which must be configured to use the proxy (manually or with a configuration script). In some cases, where alternative means of connection to the Internet are available (e.g. a SOCKS server or NAT connection), the user may be able to avoid policy control by simply resetting the client configuration and bypassing the proxy. Furthermore administration of browser configuration can be a burden for network administrators.

Access control: Some proxy servers implement a logon requirement. In large organizations, authorized users must log on to gain access to the WWW. The organization can thus track usage to individuals.

http://en.wikipedia.org/wiki/Web_proxy