Definition: Filtering Proxy
To define what this is, it might be best to start with defining what is meant by "a proxy." In the case at hand, a proxy is a service that accepts requests for web pages from a web browser, requests and receives the requested pages from the appropriate web servers and finally passes those pages to the browser. These are used for several applications, such as providing a service where a copy of a page from a slow or remote server is kept locally, to speed up access for local browsers. (This is called a "caching proxy.")
A filtering proxy is one of these services that modifies either the requests or the returned information. One application of this would be to deny access to a particular web server by simply not requesting pages from that server (based on the server's IP address or name). In this case, the proxy would return a failure code or a locally generated web page back to the browser. (It could also simply do nothing and let the connection time-out. This would not be a good thing.)
A case in which text is modified on the requested page that some people may be familiar with, is that of pages returned by search engines, where the search terms have been "highlighted". An example of this can be found with Google's "cached" items. (In this case, Google is acting as both a caching and filtering proxy.)
Proxomitron allows you to do both - permitting you to change both the request and the returned information. This gives the user the power to prevent access to certain web pages or servers, or to remove or add text to the web page as it comes in to the browser.
The access to the proxy service is done through the browser's configuration, and this process will vary for different browsers. However, most browsers facilitate this change to their configuration and the process can be determined from the browser's help facility.
Proxomitron is not an "anonymising proxy", which is a proxy that helps to mask the origin or destination of a web request. You'll have to look elsewhere for information on those.
Other filtering proxies are:
The Proxomitron is Copyright © 1999-2003 by Scott R. Lemmon.