Freedom of Web Browsing
Many employers have implemented technical restrictions at the office so that staff cannot access social network sites such as, for instance, Facebook or YouTube, during office hours. The same goes for free Web email services such as Gmail for example. Along the same lines do schools, universities and certain countries block access to “inappropriate" web sites.
There a more sophisticated technologies such as filters for restricting or blocking user’s web requests; however a corporate internal proxy server may as well be used for controlling web browsing: If the URL (Web site address) is on the blacklist the proxy won’t let users connect.
That’s why the savvy users make use of a free Web proxy such as www.NoTrack.org. There, the user enters the URL he or she wants to visit and the proxy server fetches the website. In many cases that works because the network traffic doesn't easily reveal that, for instance, Facebook, was visited. Thus, such a Web proxy server is sometimes called unblocker.
In the image below you can see where the web address of the to be unblocked site has to be entered into a form bar (the form is similar for most of these sites). Hitting the Surf Now button will take you straight to the URL you want to visit.