[taoistscholar_v2]

I must say, there's nothing but great replies here. Allow me to add my 2 cents...

Qigong just like reiki, is a quite the general term. There isn't an authority on the matter dictating any specifics or technicalities. As I'm sure you already know, the 'gong' in qigong translates into something along the lines of: work, training, practice, discipline, etc. And qi on the other hand, is quite a considerably broad notion. So it becomes quite easy for one to say this thing and that thing are qigong.

There are qigongs that focus on the immortal shen, the psyche, the internal organs, the meridians, and even the external physique. It's my opinion that although different practices might be more specific in one of these areas over another, that every qigong should, to some degree, altogether address all of these aspects. I feel this to be so based on the understanding that all those things are interconnected, and so emptying our mind will in turn benefit our ability to relax ourselves physically, optimizing the flow of qi in the meridians will influence the internal organs to function more freely, and cultivating a strong constitution that is abundant in qi, blood and physicality will result in a human system that can preserve its jing, and therefore best nourish the shen, ultimately leading to profound spiritual freedom.

To me the key features that epitomize qigong, regardless of type and style, are:
- Posture
- Breath
- Relaxation
- Intention
But I don't think simply listing them like this is enough, and so I'll attempt to describe them in more detail based on my knowledge and experience, but ultimately qigong is a discipline.. You can think and read about it all you want, and still never truly comprehend it. Some even go as far as saying that thinking about it too much will only confuse more. I role by the belief that talking about it is essential, but only in conjunction with dedicated practice, and should not be excessive. Just small bites that you can chew :P

POSTURE
It would be too difficult and over-zealous of me to go into all the specifics here, which is one very important reason why I reccomend beginners and even intermediates to train under a skilled and competent teacher. This posture I speak of is not particularly the specifics of the movement, like where your hand is, or how your weight distributes between your two legs, but rather the subtleties that facilitate the greatest relaxation, sensitivity and functional/effective force transmission and conservation throughout the entire body as a unit. Not really able to be separated from the other three aspects, but this posture deals with how the movement originates from the centre, how the tibia and fibula torque, how the joints curve, spine alignment, pelvis position, a gently lifting skull, a spacious chest, how the shoulder, elbows, etcetera, tend to be downward-seeking, even when rising up.
BREATH
There have been several different breathing methods used in qigong. Breathing is used to unite and boost the overall focus of the practice. In static qigongs it is often used to guide and consolidate intention but can also be used in other ways to essentially biohack the lungs to work more effectively, boosting our oxygen reserve within circulation. When performing movements the breath can assist the movement, maximize relaxation and the all-around interconnectedness of the system in how it moves.
RELAXATION
The relaxation might be the most difficult part of all to describe. It's nothing like our traditional understanding of the word, which is often synonymous with limp and empty. The relaxation that is principle to qigong is known as 'song'/'sung' relaxation, and is spry, supple and full. Often like you see in the posture of infants and toddlers. It has a sort of tensegrity to it that is powerful and capable of transmitting not only force but other information and sorts of feedback throughout the whole body unit. The relaxation is of the muscles and mind, but not of the framework and connective tissue. This gives a stretch and tempering of the bones and tendons that is capable of repairing and strengthening in ways external muscular-focused exercises cannot. This sort of relaxation is what must be practiced and practiced and practiced and practiced. It's a never-ending skill that can be fractally refined. You think you got it, but then as you continue to practice you realize there was still another layer, and so on. That's why you must be humble and persistent and continue to dedicatively train with a figurative smile on your face.
INTENTION
Intention is the final piece, and paradoxically enough, the final piece to it is eliminating it altogether,. But the difficulty is, intending to eliminate intention is a little counter-productive haha. What letting go of intention means is letting go of the focused mind and embodying the practice spontaneously or out of habit. In the beginning it's common to use visualization techniques, guide intention to establish tingling and sensations, focus on doing the posture, movements and breathing right. With practice, these things become more defaulted and the intention becomes more of a third party observer, scanning through the practice and 'troubleshooting', for lack of a better term. Sometimes this scanning can be done in the form of repeating a phrase or mantra in your head whenever thoughts from the monkey-mind arise. This mantra acts to simplify the entire complexity of the training into a catalyst that aligns the entire being. This way as the so-called habits form, the mind can let go of its focus on all the little sub-details that were once large areas of intentful focus. When the practice becomes 'hardwired' one can be said to be living meditation. Everything from sitting, getting dressed and opening doors, to your activities and recreation will be optimized. Not only therapeutic, but effortless and more powerful. The mind will think clearer and the emotions will be balanced.
Finally, at an even more advanced level the mind is able to fully disengage and relinquish all intent and thinking. This doesn't mean that it's completely empty per se, but just that the thoughts that do arise are not held on to, processed, or considered. This peace and tranquility is said to be the precursor of the deep spiritual experience(s).