You can see that qi is energy and is found in heaven, in the earth, and in every living thing. All of these different types of energy interact with each other and can convert into each other. In China, the word "gong" is often used instead of "gongfu" which means energy and time. Any study or training that requires a lot of energy and time to learn or to accomplish is called gongfu. The term can be applied to any special skill or study as long as it requires time, energy, and patience. Therefore, the correct definition of qigong is any training or study dealing with qi that takes a long time and a lot of effort.
Qi exists in everything. Since the range of qi is so vast, the Chinese have divided it into three categories, parallel to the three natural powers (san cai) of heaven, earth, and man. Generally speaking, heaven qi is the biggest and the most powerful. This heaven qi contains within it the earth qi, and within this heaven and earth qi lives humans, with their own qi. You can see from the diagram that human qi is part of heaven and earth qi. However, since the human beings who research qi are mainly interested in human qi, the term qigong is generally used to refer only to qi training for people.
As you can see, qigong research should include heaven qi, earth qi, and human qi. Understanding heaven qi is very difficult, however, and it was especially so in ancient times when the science was just developing. The major rules and principles relating to heaven qi can be found in such books as The Five Elements and Ten Stems (Wuxing and Shitiangan); Celestial Stems (Shierdizhi); and the Yi Jing.
Many people have become proficient in the study of earth qi. They are called geomancy teachers (di li shi) or wind water teachers (feng shui shi). These experts use the accumulated body of geomantic knowledge and the Yi Jing to help people make important decisions, such as where and how to build a house or even where to locate a grave. This profession is still quite common in China.
The Chinese people believe that human qi is affected and controlled by heaven qi and earth qi and that they in fact determine your destiny. Some people specialize in explaining these connections; they are called calculate life teachers (suan ming shi) or fortune tellers. Click to learn how Chinese medicine treats Hemophilia.
Most qigong research has focused on human qi. Since qi is the source of life, if you understand how qi functions and know how to affect it correctly, you should be able to live a long and healthy life. Many different aspects of human qi have been researched, including acupuncture, acupressure, herbal treatment, meditation, and qigong exercises. The use of acupuncture, acupressure, and herbal treatment to adjust human qi flow has become the root of Chinese medical science. Meditation and moving qigong exercises are widely used by the Chinese people to improve their health or even to cure certain illnesses. Meditation and qigong exercises serve an additional role in that Daoists and Buddhists use them in their spiritual pursuit of enlightenment and Buddhahood.
You can see that the study of any of the aspects of qi should be called qigong. However, since the term is ordinarily used today only in reference to the cultivation of human qi, we will use it only in this narrower sense to avoid confusion.