What is Qi, from the mind of an acupuncturist, lol :) On a basic note, Qi is everything that can be explained, and everything that cannot be explained. Sifu Jeffrey Yuen once described Qi as "a relationship" between anything and of anything. The late, master Kenny Gong would describe Qi as "density-change." For example the change of density between water and when it evaporates. The change in density from form to formlessness, per se. I feel that both Sifus resonated to me as beautiful responses to the question of Qi. For my personal understanding, both definitions when combined can be used to enhance one's perspective on Qi. I say, Qi can be analyzed and understood by examining the relationship between the change of density in comparison to anything you can imagine. For example, what is the state of your personal relationship between you and your partner? To an acupuncturist, it also means: what is the state of Qi between the two of you? Is there healthy, and abundant Qi; is there a sense of a balance between the two with a notion of 'give and take?' Or, does one person rob you of your essence, your Qi? Do you routinely feel exhausted after hanging out with your buddies? In this way, a practitioner can examine your relationship between yourself or another, and by tapping into the state of exchange between the Qi, as mentioned in this relationship example. Again, these examples can be taken into health care, martial arts, qigong, spiritual cultivation, inner alchemy. And the meaning takes on a deeper, more profound level of study in the Daoist or Buddhist sects, per se.