Want to feel "KI"?
Although there all already some good posts on this subject, I'd thought I add my bit.
The word/character "Ki" is used to describe many different things, some are somewhat metaphysical while others are quite tangible. It is some of the more salient aspects that keep the study of "ki" and Western science from being mutually exclusive.
Stand on one foot. For optimum balance, have your weight extend into the ground on the inside of your foot, an imaginary line between your big tow and your heel. Can you feel the energy go down through you leg into the ground? Do you feel when it is on the less stable outside?
Once you can balance, you have temporarily mastered a ki/energy exchange from your body to the ground. Magic? Unexplainable to Western science? No, just a baby step.
Now, eventually you can utilize this feature in your arms, body, fingers, and elsewhere and you are said to move with good ki. If you "disbelieve," I am sorry. There are many other aspects of this facinating concept, all of which require great effort, some faith, and a whole lot of questioning to unravel.