The fallwall is a technique used by most domino builders, including Domino Day! It is basically a steep, half-bridge where dominoes at the top of the wall topple dominoes that will fall until they hit the floor. They can easily be built with wood, glue, and supports. It's probably one of the best domino tricks out there.
There are many fallwalls that are usually referred to as an example. For instance the "The Simpsons" fallwall in CDT 2011 is a wonderful example of a fallwall and how it works. Another notable fallwall is the one used as the final in Domino Day 2004 where, in this case, the dominoes fell upon the builders of that Domino Day.