it allows exhaust gases to bypass the turbine housing to limit the amount of boost

Ok to elaborate on it some more, your turbo is powered by exaust gasses flowing through a turbine and the opposite side (compressor side), feeds air into the engine which turns into more exhaust which turns your turbo even faster. So you have this endless cycle and your build pressure up sky high and you engine goes kaboom. Now we don't want that, what the wastegate does is bleed off excess exaust gasses once you've achieved your boost level to stop the endless cycle.

Gets rid of gases.

Ask Ddavisaf to show the pics he has which shows extreme overboost.

I can't describe it. You will have to see it.

Overboost is like overrev. Both will blow it sky high.

Good answers guys.

Maybe this will help you.

How does a Wastegate work?
A Wastegate is simply a turbine bypass valve. It works by diverting some portion of the exhaust gas around, instead of through, the turbine. This limits the amount of power that the turbine can deliver to the compressor, thereby limiting the turbo speed and boost level that the compressor provides.

The Wastegate valve can be "internal" or "external". For internal Wastegates, the valve itself is integrated into the turbine housing and is opened by a turbo-mounted boost-referenced actuator.
An external Wastegate is a self-contained valve and actuator unit that is completely separate from the turbocharger.
In either case, the actuator is calibrated (or set electronically with an electronic boost controller) by internal spring pressure to begin opening the Wastegate valve at a predetermined boost level.
When this boost level is reached, the valve will open and begin to bypass exhaust gas, preventing boost from increasing.

Thanks

A wastegate regulates boost pressure. It remains closed until you hit a certain amount of boost. Lets say your wastegate is set for 15lbs it will stay closed until you hit 15lbs. At 15lbs it will open up so you dont go over 15lbs. A boost controller goes inbetween the turbo and the wastegate. The boost controller sort of acts as a wastegate as well. The valve stays closed until it sees a certain amount of boost then it opens and allows the air to reach the wastegate, then the wastegate opens. The boost controller allows you to set your desired boost without having to buy a new wastegate everytime you want to change your boost level.

Google and HowStuffWorks are great for questions like this.
http://auto.howstuffworks.com/turbo6.htm
http://www.bankspower.com/Tech_howturbowastegateworks.cfm

Steve