There is a lot of meaning in the Korean flag, which is also called Taekkuk (referring to the Yin and Yang halves of the circle in the center of the flag.
The flag consists of three parts: the white background, the red and blue circle in the center and four trigrams, one in each corner of the flag.
The white background of the flag means peace. The red and blue circle in the center is called ‘Taeguk’, the origin of all things in the universe. The central thought is perfect harmony and balance: A continuous movement within the sphere of infinity, resulting in one unit. The blue part of ‘Taeguk’ is called ‘Eum’ or in Chinese, Yin, and represents all negative aspects of the balance while the red part is called ‘Yang’ and describes all the positive aspects. The circle itself represents unity – bringing together the negative and the positive, while the Yin and Yang represent the duality. Examples of duality are heaven and hell, fire and water, life and death, good and evil, or night and day
The four trigrams at the corners (called ‘Kwe’ in Korean) also represent the concept of opposites and balance. The trigrams are heaven (upper-left) and at the other corner earth, water (upper-right) and at the other corner fire. Looking at symbols of the trigrams, you can see that they are opposites as well. Three unbroken bars (heaven) vs. three broken bars (earth), etc.
Symbolic of the nation is the white background (the land), the circle (people), and the four trigrams (the government). All three make up the essential elements of the nation.