The Korean National Flag is very philosophical. The origin comes from the oriental philosophy called Enm-Yang (Yin-Yang in Chinese). In Korea the symbol of Yin and Yang, and sometimes the flag iteslf, is called Taeguk and summarizes the thoughts of Yeok ("I Ching" in Chinese). The name means the flag of "Great Extremes."
The white background represents purity and peace.
The upper red section is called the Yang and the lower blue section is called the Um or, more commonly known, Yin. The Yin Yang is the ancient symbol of the creation of the universe and shows the differences between day and night, hot and cold, good and evil, etc. It is a representation of opposites and also a representation of how all parts are needed in order to be whole.
The tri-grams located in each corner of the flag represent the concepts of opposites and balance: Heaven, Earth, Fire, Water.