Wiktionary
n. (context computing English) A hardware server that acts as an intermediary between a user and another server, usually on the Internet.
Wikipedia
In computer networks, a proxy server is a server (a computer system or an application) 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 and the proxy server evaluates the request as a way to simplify and control its complexity. Proxies were invented to add structure and encapsulation to distributed systems. Today, most proxies are web proxies, facilitating access to content on the World Wide Web and providing anonymity.
Usage examples of "proxy server".
No plug-in is required when a proxy server HTTP is used - but then the DOI becomes just another URL, embedded in the page when it is created and not resolved when the user clicks on it.
You think I would leave sendmail running on an open port on my real proxy server?
Just minutes ago she had completed her usual log-on to the proxy server and noticed that a ciphertext E-mail had arrived.