Originally the terms meant shady side of a hill (Yin)
and sunny side of a hill (Yang)
which illustrates that they are two sides or aspects of the same entity.

Graphically this concept is expressed through the symbol (read the article)

Yin represents everything that's descending, going inside, is dark and cool; it takes care of rest, nourishment, night, winter, water etc.
Yang ascends, goes from the inside towards the outside; it's warm, light, active, protecting, day, summer, fire etc.

Mathematical or digital expression of Yin and Yang can be presented as

Combining the two, we can split it into four stages of Yin and Yang

With addition of an extra line, the Eight Trigrams (Ba Gua) are formed, illustrating transition and dynamic interrelation of Yin and Yang.

This brings the more accurate symbolic expression of Yin and Yang:

The Eight Trigrams are combined to form 64 hexagrams, whose permutations represent the continuous process of change in every aspect of nature symbolizing all possible phenomena of the Universe.
The first book that contains diagrams of the Eight Trigrams and 64 hexagrams, is the Yi Jing, Classic of Changes, which is dated as early as the time of Emperor Fu Xi (circa 1100 B.C.; the author remains unknown).

These diagrams form the foundation of traditional Chinese medical thought and the basic theories of acupuncture, the Yin-Yang theory and the theory of the five elements.

The five laws of Yin & Yang:

- Opposition.
Everything has two opposite aspects. Yin & Yang struggle with and control each other.

- Inter-dependence.
Yin & Yang define each other and therefore one cannot exist without the other. (If there is no down, which way is up?)

- Mutual consumption & support.
Yin & Yang each give of themselves to nourish the other.

- Inter-transformation.
YIn can become Yang and Yang can become Yin. In fact, this is inevitable if the growth of one or the other is uncontrolled.

- Infinite subdivisibility.
There is always an element of one in the other. Anything can be subdivided again and again.

- Neither Yin nor Yang is good or bad;
- they are 2 opposites that are supplemental;
- they are two aspects of the same entity;
- they transit into and are dependent on each other;
- disbalance between Yin and Yang is Illness, separation of them is death...

After a while Yin becomes Yang and Yang becomes Yin, like day becomes night, summer becomes winter and action becomes rest.

No matter what is the level of organization we refer to (from elementary particles to human beings and even up to galaxies), one of the fundamental laws of Nature is that of the permanent interaction between the two complementary forces, YIN(-) and YANG(+). All the processes and phenomenons of Nature are the expression of the interaction of these two principles.

	YIN	YANG
Tendency	Extension, dilatation	Contraction
Position	Exterior	Interior
Direction	Downward	Upward
Temperature	Cold	Hot
Gender	Feminine	Masculine
Element	Water	Fire
Season	Cold, winter	Tropical, summer
Structure	Space, mass	Time, energy
Orientation	Centrifugal	Centripetal
Color	Violet, mauve	Red
Weight	Easy	Heavy
Atom	Electrons	Protons (nucleus)
Chemical element	Potassium, Calcium, Oxygen, Azoth, Sulfur, Phosphor, Silicon, Iron, Strontium, Lead, Aluminum, Cobalt, Molybdenum, Tin, Silver, Chlorine	Sodium, Hydrogen, Carbon, Magnesium, Arsenious, Lithium, Quicksilver, Uranium, Neon, Chromium, Nickel, Copper, Palladium, Gold
The living world	Vegetal	Animal
Plants	Salads, legumes, fruits	Cereals
Aliments	that contain much water;	that contain little water
	rich in potassium;	rich in sodium;
	rich in glucides	rich in proteins
Taste	Sour, piquant, peppery, astringent, softly acid, sweet	Salty, bitter, alkaline
Nerves	Ortho sympathetic	Para sympathetic
Neurochemical Basis	Inhibition	Excitation
Vitamins	C,B2,B12,Pp,B1,B6	D,K,E,A
Zodiacal signs	TAURUS, CANCER, VIRGO, SCORPIO, CAPRICORN, PISCES	ARIES, GEMINI, LEO, LIBRA, SAGITTARIUS, AQUARIUS
Metabolism	Anabolism	Catabolism
Pace	Slow	Fast
State	Passivity, static, inertia	Activity, dynamic, movement
	Sleep	Wake
Blood pressure	Hypotension	Hypertension
PH	Acid	Alkaline
Humidity	Wet	Dry
Other attributes	Expansion	Pressure
	Quiet	Sound
	Low	High
	Bigger	Smaller
	Long	Short
	Horizontal	Vertical
	Soft, fragile	Hard
	Root	Top
	Down	Up
	Periphery	Center
	Plural	Singular
	Subordinated	Leading
	Inorganic	Organic
	Unruly, unrestrained	Retained, controlled
	Earth	Sky
	Moon	Sun
	Night	Day
	Dark	Light
	Gas	Solid
	Extrovert	Introvert
	Woman	Man
	Magnetic	Electric
	Atomic energy	Nuclear energy
	Ultraviolet	Infrared
	Short waves	Long waves
	Negative	Positive
	Concrete	Abstract
	Sperm, Spermatozoon	Menstrual blood, Ovule
	Bleu, indigo, violet	Red, orange, yellow
	Moon	Sun

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