A pressure washer, simply put, is a pump that boosts normal household pressure of 60 - 70 pounds per square inch up to 1,000 pounds per square inch, or more. The resulting high pressure water stream generates a cleaning action that can be used to remove loose paint, mold, grime, dust, mud, and dirt from surfaces and objects such as buildings, vehicles, fences, walks and driveways.
Power washers are powered by either gas or electric motors (the one used in this video is electric). Many can be fitted with different nozzles that eject water in a fan pattern, while others emit a thin jet of water, which spirals around rapidly (cone pattern). Some pressure washers, in combination with a particular nozzle, allow detergent to be introduced into the water stream, assisting in the cleaning process.
When using a pressure washer, keep in mind that, if held too close to the surface, especially with wood, the high velocity water jet can etch or otherwise damage surfaces.