Proxy means one thing acting on the behalf of the other. A proxy server, is a server that operates between your browser and a remote Internet connection used for a variety of purposes.
The proxy server at your school allows the network administrators to control internet access on their machines among other things. In order for you to change the Facebook block, you would have to know the passwords and procedures to access that specific system.
Answered Nov 24, 2010
Edited Nov 24, 2010