Just as with communication between people, a proxy is a computer server that makes a conversation on behalf of someone else. In the case of computers, the someone else is another computer. In the case of computers speaking to each other by proxy, the nature of the conversation is based on data transmissions between a workstation computer and a server on the internet. There are a few different reasons to have a proxy in place in a setup where there are lots of computer systems that are allowed internet access. One of the biggest advantages to a proxy server is the security aspect of the connection provided by the server. Visiting a web site is more behind the scenes than most users realize. Viewing a web site is not just a passive experience of viewing a page on your computer screen. Going to a web address makes a connection between your computer and the remote server and data packets are downloaded to your computer from that remote server.
Some of those data packets can be more than you expect. An example would be a web server that has been infected with a virus that sits on the server and exploits vulnerabilities in the computers that visit the site. By using a proxy as an in between connection, the server that an endpoint computer connects to is never really connecting to the computer making the connection. The data packets are requested by the proxy, then responses are received by it and passed along to the client computer in place of a direct connection. By this process, end user computers are isolated and protected from the various hazards that can present themselves to systems in contact with the internet. It is by this quality that a proxy server is most beneficial to a corporate network.