efinition: In feng shui, as in Chinese medicine, CHI is the term for the universal energy, or the energy that permeates everything around us. This feng shui term applies to the energy inside your body, as well to the energy inside and outside of buildings.
Chi, or feng shui energy, is manifested in yin and/or yang characteristics and in a variety of forms according to the five elements feng shui theory. In feng shui, Chi manifests itself in different shapes, colors, intensity, etc.
The main goal in feng shui is to channel, or direct the Chi inside your home so that it nourishes and supports a good flow of Chi inside your body.
The quality of Chi you always want to have around you is the vibrant, alive, fresh Chi, also called Sheng Chi in feng shui; and the quality of Chi you better avoid are Sha Chi and Si Chi (sharp and attacking or low and depressing feng shui energies.)
Most common feng shui Chi blockages in a home are Chi blockages at the main door, such as when the main door opens into a wall, for example; as well as Chi blockages in cluttered garages and closets.
Most common feng shui Chi leakage (loss of feng shui energy) occurs when there is a direct door alignment in a home, especially of the main door with the back door, as well as a direct alignment of a big window with a door.
Identifying the Chi flow in your home is easy if you visualize Chi, or feng shui energy, flowing into your home as water. Would the water flow smoothly and nourish all areas of your home or will it get blocked and stagnant in many areas?
Do your best to create a home with a smooth Chi flow, as the flow of Chi in your home sooner or later will reflect in the flow of Chi in your body.
Also Known As: Ki, Qi, Prana, Life Force
Examples: The flow of Chi, or feng shui energy, in your office is constricted; you do not have enough vibrant Chi to support good health and well-being.
PSI-"Subtle energy" redirects here. For the mystical concept of psychospiritual bodies overlaying the physical body, see Subtle body.
The term energy has been widely adopted by writers and practitioners of various forms of spirituality and alternative medicine   to refer to a variety of ideas often, though not always, conceived as "fields" surrounding the earth or any living thing, supposed to be directly perceptible and accessible to the human mind as "auras", "rays", "fields" or "vibrations".  There is no scientific evidence for those kinds of energy or fields, indeed energy is very well defined in science.  The term was borrowed from physical science as an analogy where, for example, in physics, measurable quantities of energy are associated with a variety of observable phenomena including waves, potential fields, and even matter itself. Unlike in the physical sciences, spiritual energy is not necessarily considered by those who believe in its existence to be something that can be directly measured or observed in a laboratory. Still, many believers in spiritual energy have used the discoveries of modern physics including relativity and quantum mechanics to support their beliefs in both allegorical and pseudoscientific ways. 
In many cases "energy" is conceived of as a universal life force: to this extent "spiritual energy" theories resemble vitalism  and may even invoke the Luminiferous Ether of Victorian physics.  Additionally, or alternatively, such notions are often aligned with or derived from conceptions found in other cultures, such as the Chinese idea of Qi and the Prana of the Upanishads.  Many such ideas arise from the primitive idea of life as breath - a relationship implicit also in the word "spirit".
Such a usage is already evident in William Blake's The Marriage of Heaven and Hell (1793);
"Energy is the only life and is from the Body and Reason is the bound or outward circumference of Energy. Energy is Eternal Delight." 
Blake's alignment of energy with affective emotion is noteworthy, for it depicts energy as the psychic continuum that unites body and mind, thus reflecting Plato's celebrated tripartite division of the human psyche into the appetitive, the spirited and the rational.  Such an integration of "energy" into systematic esoteric expositions of the universe and/or the human psyche is frequently found combined, as in Kundalini and Theosophy, into an account of a hierarchy of "inner planes" or "subtle bodies". 
When you delve into Chinese medicine, physical energy is *at a minimum* split into three categories: chi, jing, and shen. This is a MAJOR over-simplification. Quite simply, there is no way to elaborate on this adequately.
Chi is a concept that even the most well-meaning and well-studied Westerner has a hard time grasping - even professionally-trained Western acupuncturists and medical qigong practitioners.
It's impossible, so i've learned from my formal studies in Chinese Medicine, to cull out physical chi-type enegies from mental chi-type energies, although occultists very commonly make this distinction with chi v. psi type conversations. In medical applications, there is no such distinction.
Now, almost everyone who studies chi cultivation practices honestly and intently will eventually have massive spiritual and psychic pay-offs, usually without intending to do so. It is just the natural progression, observed for thousands of years. All qigong adepts have what we would term as psychic abilities; they develop them through "physical" chi cultivation. Chi is Jing which is Shen which is Spirit. They are different but the same, impossible to seprarate except when theorizing.
Energies do "feel" different, of course, and are different too. They vary in density, the techniques vary, the applications vary, some are slower, more solid, more etheric. You can use different energies for different goals, etc. There is absolutely no argument that different energies do exist, but i think it's an over-simplification to delegate chi into the physical only.
I know that some of the more advanced practitioners probably know what i mean, and maybe it's just not the appropriate forum for a higher-level discussion of what chi really is and isn't. That's the stuff of YEARS of qigong and Chinese Medicine. Maybe it us just easier to say that chi is physical, knowing that this is a half-truth.
Many experts define chi as communication between your organ systems and your environment, your body's pattern and sense of rythym, a regulatory system, and a means to communicate from energy field to energy field - from the Universe to the Earth (my very much non-expert definition, or horribly incomplete definition).
The worse thing an energy practitioner can do when experimenting with different energies is to "visualize" the energy, to make a false mental picture of what you "should" be experiencing, and have a preconcieved notion about what you "should" be feeling, what color the energy "should" be, how it "should" move, etc.
FEEL the energy. Don't judge it. Don't visualize it. You will only get a product of your mind through visualization - and your mind is a poor teacher. If you FEEL nothing, don't be hard on yourself. Intend to feel the energy (not visualize. Intend). Relaxation + Alignment + Intention = Energy Flow. Maybe a bibliography of good energy books and resources would be in order (www.energyarts.com).
A little abstract and a terribly-worded failure in shedding light on a concept that is meant to be solely experienced, not written about...