"Proxy" is no longer just some obscure legal term. Now internet proxies are used by everyone from students and workers to people living in countries like Iran or China where the government censor their citizens traffic.
When you surf the web you give an enormous amount of information to the websites you visit: ip address, location, referrer, browser, resolution, isp, etc. The most identifiable bit of information here being your ip address. By putting a phproxy between you and the websites you visit your ip remains hidden.
Below are some useful php proxy resources, from online proxies to the scripts to make your own.
Free Proxy Site
PHP Web Proxy
If you are a webmaster wondering what happened to the popular PHProxy read this.