The spelling Chi Kung (Wade & Giles) is outdated and was developed as a transcription around 100 years ago in Cambridge. Today we know how Chinese people emphasize and the current romanization is called Pinyin. It is also called Tai Ji instead of Tai Chi.
There are schools that say Qi Gong is about energy or breathing, but both are not entirely accurate. The fact that one tries to delineate the whole is typical of our Western conception and absolutely cramped.
After traditional Chinese medicine (TCM) and classical Chinese medicine (CCM), which by the way are different from the commercialization of the Sino-Republican concept, the CCM is closer and more authentic to our Wudang understanding. Both teachings state the following:
Qi Gong can be translated very precisely as a breathing practice that brings us energy. However, here the medical conception differs from the esoteric one. Energy is not obtained from the pleasant comfort in which the ignorant like to crawl. Qi Gong is a soothing and enjoyable practice where you learn to stand properly, breathe properly and relax. The focus is inside out and the practitioner gains control over himself. The path is to change, and for any organism, change is never pleasant.
Qi Gong is the foundation of the inner martial arts and health, the circulation created by these exercises gives the body the necessary energies to become stronger. Qi Gong is also the only practice recommended for healthy and sick people.