Qi

Qi, or in some cultures, such as China and Japan, Chi or KI, respectively, is the energy that flows through all living beings.

Uses
Qi is generally used for meditation and in case of extremes combat. There are those, such as Tan Zang have been become so in tuned with their Inner Power that they can slow down their aging and become attuned with nature. To be able to tap into one's Inner Power, one trains both the body through training and the mind through meditation.

Trivia

 * When Tam Sung first met Jack in the future, he assumed Jack was still young because of his mastery of Qi, though the truth is because of being sent into the future. Considering Jack's remained an adult for 50 years after being sent to the future, it is likely exposure to time travel magic altered his Qi in some way.
 * During Jack's training with the Shaolin monks under Master Chu, he would have learned of how to tap into his Qi. Centuries later under Chu's son Tam Sung, the monks had refined their training, enabling them to accomplish physical feats through Qi alone.
 * Some of the feats of Qi shown in the series are based on actual Shaolin training methods, such as hitting the bell without physically touching it.