In Chinese this is the word "air". The difficulties of the Chinese language lies in that a single word has intrinsic meaning that is different in special contexts. In Feng Shui, qi is like energy, more often than not organic in nature, that flows in space. Our five senses can feel the existence of qi.

Vibrant life energy. When we see that a place is full of life, it is filled with sheng qi.

Killing energy or harmful energy. When we feel that we are being attacked by something invisible we are feeling the existence of sha qi.

Literally feng means wind and shui means water. In Guo Po's Book of Burial :

Qi is dispersed by wind and retained by water. Qi in this context refers to sheng Qi. It is dispersed by wind but is retained by the existence of water. Feng shui is therefore the study of how to choose a site devoid of attack by dispersing wind and maintained vibrant by the presence of water.

The dragon is a legendary creature. In China the dragon symbolizes the Emperor. In the Feng Shui aspect it symbolizes vital energy that exists on earth. Its existence can be traced in mountain ranges. It can also be traced in rivers and streams. Mountains are referred to as mountain dragons while waters as water dragons. Beautiful mountains and waters are vibrant dragons and are capable of emitting sheng qi. Ugly mountains and waters are sick dragons or even dead dragons and are capable of emitting sha qi.