Definition by the Feng Shui Society:

Feng Shui is the practice of analysing and influencing the interaction between people buildings and the environment in order top enhance the quality of life. Originating in ancient China, its basis chi which is vital energy present in everything.

Chi can be defined as the subtle flow of energy linking all thing in the universe. It is an energy that is finer and more subtle than electric magnetic or thermo-nuclearenergies.

"Chi is present in everything"

Feng Shui literally means "wind-water" this indicates how energy (chi) moves. Beneficial Sheng chi moves in a meandering way; like water in a stream or air in a light breeze.

So to "Feng Shui" means to balance and harmonise our interaction with the environment thorough manipulating the qualities of chi.