Sun Yi's Tae Kwon Do family site.

The Korean national flag is called TaeGukKi or TaeKukKi.
 The meaning of Korean National Flag is very
philosophical. The origin comes from the old oriental
philosophy called the theory of Eum-Yang, in chinese
pronounciation Yin-Yang. Yin means negative, dark, and
cold; Yang means positive, bright, and hot. The idea of
Yin-Yang is supposed to be originated from the old
Korean philosophy of SamSin meaning three gods.
A very old book called JooYuk or IChing in chinese,
which was written by (a) chinese several thousands
years ago, claims all (physical or virtual) objects and
events in the world can be expressed by the movement of
yin and yang.
For example, minus(-) is yin while plus(+) is yang; the
moon is yin while the sun is yang; the earth is yin and
the heaven is yang; a woman is yin and a man is yang; the

 night is yin and the day is yang; the winter is yin and
 the summer is yang, etc.
Yin and yang are relative, which means A can be yin with
respect to B while A can also be yang with respect to C.
For instance, the spring is yin w.r.t. the summer and it
is at the same time yang w.r.t. the winter. Yin and yang
are opposite and struggle each other while they
cooperate in harmony. The harmonious state of the
 movement of yin and yang is called TaeGuk, Taichi in
chinese, which is also the name of the Korean national
flag, i.e. TaeGuk-Ki or TaeKuk-Ki. Ki means a flag.
(See the similarity between the concept of
Yin-Yang-Taichi and the dialetics of
thesis-antithesis-syntheis.) The upper half circle, red,
of TaeGuk means yang and the lower half circle, blue,
means yin. They stand for the state of harmony of yin
and yang.

The symbols, called Kwe, in the four corners, mean the
principle of movement and harmony. Basically, each Kwe
cosists of three bars that can be either broken or
unbroken bars. A broken bar stands for yin while an
unbroken bar stands for yang. For example, the upper
left Kwe, called Kun or Keon, is composed of three solid
unbroken bars. And the lower left Kwe, called Yi, is
composed of two unbroken bars and one borken bar in
between. Since one bar can be either broken or unborken,
i.e. same concept as bit as in the binary computer world,
 three bars can express 2**3 = 8 combinations. If you use
 four bars you can express 2**4=64 combinations; 10 bars,
 2**10=1024, etc. Therefore the more bars you use the
 more different situation you can express with Kwe.
Among so many states of Kwe, i.e. principle of movement
of objects and events, four basic Kwe are used in the
Korean National Flag. Those are Kun meaning heaven, Yi
meaning fire, Kam meaning water, and Kon meaning earth.
Each of them symbolizes a different state of movement.

The white color of background
stands for the peace and the purity of the Korean
people who have loved to wear white colored clothes.
Therefore, the Korean people have been called the
white-clad nation.
To conclude, the symbols, Yin, Yang, Kun, Yi, Kam, and
Kon, express the principle of the movement of all
objects in the universe and the movement of the
universe itself. It also stands for peace and harmony.