Hair washing
Hair washing is the cosmetic act of keeping hair clean by washing it. To remove sebum from hair, some apply a surfactant, usually shampoo (sometimes soap) to their hair and lather the surfactant with water. The surfactant is rinsed out with water along with the dirt that it bonds to.
There are dry shampoos; powders which remove sebum from hair by soaking it up prior to being combed out.
Hairdressing
Most hairdressers in Canada, US and Europe and Latin America, offer hair wash as a service before or after a hair cut. This is usually done to make hair more manageable for the hairdresser performing the hair cut. After a hair cut, it can remove loose strands of hair. It is also a relaxing practice, and many clients enjoy a hair wash as part of a hair cut.
Hairdressers use specialized basins to perform a hair wash; these can be either forward or backward style. In the backward version (the more common), the client sits in a chair, and leans their head back into a sink, with the hairdresser standing behind them. In the forward version, the client leans forward over a sink, and the hairdresser stands over them to wash their hair.
In some parts of the world, such as China, it is not uncommon to see what is referred to as an 'upright' shampoo. In this style, the client sits in a chair, while a hairdresser applies shampoo to their hair and adds water. They then rinse off into a basin.