My Top 3
A proxy is a computer system or router that breaks the connection between sender and receiver. Functioning as a relay between client and server, proxy servers are used to help prevent an attacker from invading the private network. Proxies are one of several tools used to build a firewall.
The word proxy means “to act on behalf of another,” and a proxy server acts on behalf of the client and the server. All requests from the clients to the Internet go to the proxy server first. The proxy evaluates them, and if allowed, re-establishes the requests on the outbound side to the Internet. Likewise, responses or initial requests coming from the Internet go to the proxy server to be evaluated. The proxy then talks to the client. Both client and server think they are communicating with one another, but, in fact, are dealing only with the proxy.
Example of proxy sites