Image from Bernd Helfert
Also qi, ki, or chi. An esoteric concept from Old Earth Chinese culture, widely used from the Agricultural Age onwards. Prana, vayu, orgone, od, 'life force', ruah, and zoei are equivalents in other cultures. Ch'i is conceived of as the vital principle, or life-force that flows through living bodies and links them to their surroundings. It is envisioned as something that can be manipulated and cultivated through disciplines such as Internal Alchemy, Neotaoism, Hatha Yoga and certain Martial Arts. Ch'i is an important concept in Penglaiese, Chin, Genetekkerese, Genen, and Zoeific Biopolity memeticities and is a core technique of bioaugmentation and self-development there and elsewhere.
Ch'i and similar ideas have no basis in the sciences, and on this account many simply discount it as a superstition or as an outmoded prescientific idea that is not worth using or considering seriously since it does not exist in the form originally described (outside of virches or artificial environments that are specifically meant to mimic the original vision of it). On the other hand pragmatic materialists may regard ch'i as a useful concept that integrates aspects of physics, physiology, and psychology into a simple construct for ease of manipulation. Such a point of view is widespread and may be seen in the practices of members of groups like Ecos Ascending. In contrast mystics may be more interested in using ch'i as a springboard for spiritual rather than physical development, with or without any discussion of whether it is 'true' in anything other than a spiritual or philosophical sense. Still others simply treat ch'i as a physical reality, on par with magnetism or gravity, though those who do so may be regarded by others as superstitious or simple-minded.
Though the idea of ch'i originated with human baselines, and is still more common with bionts generally and humans in particular, there are clades and cultures of cyborgs or vecs who that also use ch'i or similar concepts, though the details of beliefs and practices about it can differ quite radically from the original Old Earth human version. Some such are inspired by or descendants of the original, and others are parallel independent inventions (or as some practitioners insist, discoveries). There are of course any number of cybercosms in which the core rules for interaction include ch'i or something like it, and the setup of some angelnet systems can allow a fair simulation of the traditional concept of ch'i.
However conceived, ch'i is a persistent belief or idea, and is widespread in Terragen cultures through to the Current Era, particularly in bioist regions.