The word
Qi (氣), older spelling chi, is written with a character that early forms associate with vapour or steam, often paired with the element for rice. The root sense is breath and the visible mist of it, extended to whatever animates and moves.
"Energy" imports a physics concept that isn't there. "Vital breath" or "vapour" gets closer. In classical Chinese the word does a lot of ordinary work too: weather is qi, mood is qi, the air in a room is qi. It wasn't originally an occult term.
It's barely in the Tao Te Ching
Worth saying plainly, because popular accounts imply otherwise. Qi appears in only about three chapters: 10, 42 and 55. Chapter 42 has the cosmological line about the ten thousand things carrying yin and embracing yang, with the blending of qi producing harmony. Chapter 10 asks whether you can concentrate your breath until it's supple as a baby's.
That's most of it. The Tao Te Ching is not a book about qi, and if someone tells you Taoist philosophy is fundamentally about energy cultivation, they're describing later religious Taoism rather than the classical text. Our guide to the two Taoisms covers that split.
The Zhuangzi does more with it, particularly the "fasting of the mind" passage in chapter 4, where listening with qi rather than with the ears or the mind is offered as a practice.
Where it became central
In the traditions that grew up later: Chinese medicine, acupuncture, qigong, tai chi, internal alchemy. There qi is a working concept with a whole descriptive apparatus, moving through meridians, present in organs, deficient or stagnant or excessive.
Those systems are internally coherent, thousands of years old, and still practised by many millions of people.
The honest evidence note
Qi has not been detected as a physical quantity, and the meridian system doesn't correspond to any anatomical structure. Controlled trials of acupuncture generally find that needling produces effects, and that the effects don't depend much on hitting the classical points, which is difficult to square with the traditional theory.
What does hold up: the practices themselves. Tai chi has decent evidence for balance and fall prevention in older adults, and qigong and breath work show measurable effects on stress markers. Slow coordinated movement and controlled breathing do things to a body, whatever we call the mechanism.
So the practices can be worth your time while the metaphysics stays unproven. Plenty of practitioners hold exactly that position without discomfort.
Reading around it
For the classical texts themselves, the translation guide and the Zhuangzi. For the ideas that the Tao Te Ching actually is about, see wu wei, ziran, and yin and yang. 365 Days of Tao carries the complete text a verse a morning.
Common questions
What does qi mean?
Breath, vapour, or vital air. The character is associated with steam or mist. 'Energy' is the common translation and the least accurate, since it imports a physics concept the original doesn't have.
Is qi in the Tao Te Ching?
Barely. It appears in about three chapters, mainly 10, 42 and 55. The Tao Te Ching is not a book about qi, whatever popular accounts suggest.
Is qi real?
It has never been detected as a physical quantity, and meridians don't match any anatomical structure. The practices built on it, particularly tai chi and qigong, do have measurable effects on balance and stress.
What's the difference between qi and chi?
Nothing. Chi is the older Wade-Giles spelling and qi is the pinyin one. Same word.
Do I need to believe in qi to practise tai chi?
No, and many practitioners don't. Slow coordinated movement and controlled breathing have effects regardless of what you call the mechanism.