Does your school censor some sites? Is Facebook blocked, and you'd like to unblock it? You have to visit Facebook, but its blocked by the school administrators? Then carry on reading.
An unblocker is a kind of gateway that pass information between the computer you're on and the site you want to go to. The unblocker goes to the site you want on your behalf, downloads the page, and forwards it to you. So the site you want to access only sees the unblocker's IP. So in effect you are visiting sites in an indirect way. School filters only see you visiting the unblocker, not the site you actually want.
An alternative method of unblocking Facebook in school is to set up your own unblocker tool. This is harder than using an unblocker but it pays off because you're in control. How to do this is beyond the scope of this article, but if you search for "How to make your own proxy" you should find some guides. You can also make money from your unblocker by letting people advertise on it.
Some other ways to unblock Facebook are by using translator sites, like Google Translate or Babelfish. Also try Google's cached copy of the site. Although, it won't let you to log in using these methods, so it's still best to use unblockers for Facebook, though these tips are good with most websites.