Feng Shui is an old Chinese practice that uses the laws of Heaven (astronomy) and Earth (geography) to help people improve their life receiving positive Qi (energy).
The original designation for this discipline is Kan Yu, literally: heaven and earth. Essentially, it is the observation of heavenly (time) and earthly (space) forces and how each Qi interacts with the other. Balancing these forces is the purpose of Feng Shui.
The words Feng Shui are literally translated as "wind and water". This is a cultural simplification of the Zhangshu - Book of burial - by Guo Pu (276-324) of the Jin Dynasty, where it appears for the first time.
In the Chinese culture, the smooth breeze and the calm water have always been associated to a good harvest and a good health, whereas the rough winds and the suspended water have been associated to hunger and disease. Therefore, "good" Feng Shui means good fortune, and "bad" Feng Shui means difficulty and displeases.
Feng Shui is not a superstition. It is the art and science of understanding the energies and forces of the nature to design the houses and the workplaces so that they act with the surroundings instead of acting against them. It helps us to live in harmony with the surroundings promoting the flow of positive energy and neutralizing or avoiding negative or destructive energy.
The main directive of Feng Shui is to take the maximum advantage of the energy flows (Qi). These flows are influenced by the forms and the elements that compose the world. This discipline is based, among other things, on the theory of the 5 elements (Water, Wood, Fire, Earth and Metal) and the principle of Yin and Yang.