"Clint: Ki is the Japanese name for universe lifeforce energy (ULE); just as qi or ch'i are the Chinese names for it. itaki is the Pueblo indian name for it, nuwati is the Cherokee name for it, and mana is the Hawai'ian name for ULE."
There's also prana and ruach. But all those are just names, not explanations or even descriptions. I had a book (now lost) by an aikidoka who claimed there is no such thing as ki; it's all physics, anatomy, psychology and confidence. I don't agree entirely, but a lot of things the aikido people call "ki" is a mixture of those things. Plus momentum & timing & who knows what. Especially the tricks people show you to demonstrate ki/chi are not always done with chi.
Is the chi that circulates through the acupuncture meridians the same as the chi that you use to heal? That a small person can use to throw a large person? (Do those meridians even exist except as a theoretical construct?)
There are some qi gong excercises you can do that will let you feel the chi in your hands, and after a lot of practice you can feel it in your arms & then your whole body. And it seems to be related to blood circulation. But what is it, aside from a word that makes it possible to talk about certain undefined phenomena?
That's why I said "whatever it is." It's a mystery. And a bit of thread drift, I suppose.