Pressure washing per the wikipedia is as follows.

Pressure washing  is the use of high-pressure water spray to remove loose paint, mold, grime, dust, mud, and dirt from surfaces and objects such as buildings, vehicles and concrete surfaces.

Pressure washing is what you have more than likely used at your house or home before. It uses some high-pressure water to blast onto the surfaces you are cleaning. It uses cold water and doesn’t heat up the water before shooting it out. This regular temperature water still does an amazing job at blasting and washing away dirt but doesn’t perform as well against moss, mold, or other tough stuck-on substances. It still does an amazing job, but might not be able to get rid of tough stains on concrete. Hardware stores. sell pressure washer machines. They can be electric or gas-powered. You hook them up to a water source. They are used for pressure washing OUTDOORS such as house siding, dirty RV’s, wood decks, & concrete. Because you are using water pressure to clean-its usually not necessary to use soap. If your driveway is oil stained-you can use a cleaner in conjunction with the pressure washer. The same applies to dingy deck boards- deck wash is available if necessary. The pressure washer has different settings to control the force of the water pressure.