Qigong is a term used to describe physical, mental, and breathing exercises for health. Qigong exercises are classified into static and dynamic postures. Taking a broad look at the history of qigong practice, you first must understand that at the time these practices were developed; they were not called qigong. For the daoist and Chinese medical doctor there was dao yin, and for the buddhist there was the yi jin ching, for example.
Medical qigong classifies those practices based on traditional Chinese medicine theory with the goal to prevent or cure illness. The types of practice would depend on the condition of the practitioner with the goal of restoring balance and health.
Daoist priest's developed a system of alchemy based around the trigrams of the Bagua. These systems were seeking the elixir of life. The exercises focused the practitioner on the lower Dan Tian, an area below the navel, with the goal of creating an elixir field that could be manipulated through sexual or other physical practices.
The Buddhists were more concerned with liberation from reincarnation and self-observation then the Daoist. The buddhist exercises were more meditative seeking a state of pure consciousness or a "sound mind in a sound body."
The Confucians believed that by creating healthy family you would create a healthy country. This starts with the health of single person. Therefore, it was the responsibility of every individual to exercise daily and to develop into a virtuous person. The exercises are often the same as exercises from other systems, but the goal of the student is to cultivate benevolence, sincerity, respect, and other virtues.
Martial qigong developed to improve the efficiency of the muscles, bones, and ligaments to use in a fight. Exercises developed not only physical strength, but mental strength. The ultimate goal was to balance the hardness and the softness by developing the body to be strong on the outside while maintaining suppleness on the inside. The actual term, qigong, probably arose during the Cultural Revolution as an attempt to integrate Chinese medicine practices with Daoist, Buddhist, and Confucian methods of self-cultivation. While the term qigong is relatively new, the practices we now call qigong are quite old. The first explanations and illustrations of such exercises coming from the Zhou Dynasty (122 - 255 BCE). The most famous of these early illustrations is the Dao Yin Illustrations, which depict 44 human figures (drawn in color) with different postures and short captions drawn in black lines.
The Huangdi Neijing--the earliest Chinese medicine reference--summarized theoretical and practical knowledge on health and was the primary reference material on qi and health promoting exercises for centuries. Qigong is a practice that has taken on mythic qualities. In the early 1950's Liu Guizhen, a doctor, used his family's method of qigong practice to cure himself; He wrote a book to promote his system. Later, madam Guo Lin is said to have cured herself of uterine cancer. She was diagnosed at the age of forty and suffered through many operations and setbacks. After eight years she began to practice qigong methods in the park for two hours a day, and within six months she claimed to be cured of the cancer. Stories like these cross the practical aspect of physical exercise with mysticism that promises miracles. Rather than the movements of a qigong sequence simply being movements, they turn into some sort of spell. I guess that moving this arm this way, followed by that way, will generate a certain response that creates a healing effect on the cells of the body. But, it will only work if you breath a certain way, at a certain time of day, and if you are not healed, then you must have been doing it wrong or chosen the wrong system, or your teacher was a flake. My vote is on the last one.
Qigong is not a magic spell. A more accurate term is calisthenics. Calisthenics are defined as an exercise used to achieve bodily fitness and grace of movement; a definition that is not far from the practical definition of qigong presented below. The need to move something as practical as an enjoyable exercise routine into something that will cure any disease, or cause you to become immortal is a mystery to me. Qigong forms are easy to do, and are accessible to people in many age groups or physical condition. There are sitting, standing, and lying qigong forms that can relax or energize the most harried practitioner. Set aside the mythical stories and try to arrive at a practical definition of the term. Qi means breath, and gong can mean work, merit, achievement, or practice. So at its most literal qigong is breath work or breath practice. A practical definition is: An exercise set emphasizing breathing techniques and designed to achieve bodily fitness.