Qi is best understood in relation to Yin and Yang. The principles of Yin and Yang theory are based on dynamic balance via the movement of Qi energy. Qi is invisible, only seen through the influence it has on living beings and material forms.
Magnets are an example of Qi in accordance with Yin and Yang: One side is north; the opposing side is south. They push and pull, but when spun together they are a generator of electricity.
In Traditional Chinese Medicine (TCM), it is believed that all vital functions within the body are also governed by the changes and movements of different types of Qi, including Yuan Qi (primary Qi), Zong Qi (chest or lung), Ying Qi (nutritive), and Wei Qi (defensive Qi).
Qi is thought to run through energy pathways in the body known as meridians. When the body is out of balance, TCM practitioners look at what symptoms are occurring and what Qi pattern is presenting itself.