What is a proxy web site?

A Proxy Web Site is mostly being used by users to access blocked websites at libraries, work, colleges, universities ,school etc... The Proxy Site also provides you with anonymity and some more extra security add-ons. By using the a proxy site, you can "mask" your real IP address with the ip from the proxy site,in other words you don't let others to see your real IP as you will be using the Web Proxy's IP. Is that all? No, by using a proxy site you will be able to access several social networking websites and not to say that you will be able to watch online videos on YouTube or DailyMotion as most of the Proxy Sites support javascript and videos!