Let’s start with a few of the many different Dictionary meanings that are out there:
1. The Chinese art or practice of positioning objects, especially graves, buildings, and furniture, based on a belief in patterns of yin and yang and the flow of chi that have positive and negative effects : The Free Dictionary by Farlex
2. A Chinese system of designing buildings or arranging rooms according to special rules about the flow of energy that is though to influence people’s lives : Macmillan Dictionary
3. A Chinese geomantic practice in which a structure or site is chosen or configured so as to harmonize with the spiritual forces that inhabit it; also : orientation, placement, or arrangement according to the precepts of Feng Shui : Merriam-Webster Dictionary
Bottom line is: Feng Shui is a System of bringing together the 5 elements of Wood, Water, Metal, Earth and Fire (and the energies they emanate) in an environment to bring forth balance and harmony a person desires by using compass directions.
Not very scientific I know. However, you can not see the wind, yet you can feel it. People have gut feelings all the time, yet it is hard to describe exactly what that feels like or where it comes from. You can not see the electricity that zapped you from an electrical outlet or a battery. Better yet, the wireless computer working from electricity flowing through the air that can not be seen but you know is there is another great example.
All things are made of energy. Feng Shui is about balancing that energy for harmony and greater living for you.