What does a proxy server do? What is a proxy server good for?

In computer networks, a proxy server is a server (a computer system or an application) that acts as a link/connection between two devices 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 packing of data and functions into a single component to distributed systems. Today, most proxies are web proxies, facilitating access to content on the World Wide Web and providing anonymity

Communication between two computers (shown in grey) connected through a third computer (shown in red) acting as a proxy. Bob does not know whom the information is going to, which is why proxies can be used to protect privacy.