The National Flag of South Korea is called Taegeukgi. The flag was first established as a symbol of the Kingdom of Korea on May 22nd, 1882 however it was not until 1948 that it was officially adopted as the National Flag of South Korea.
The blue and red circle in the centre is called Taegeuk which represents yin and yang and the need for opposites to exist. This symbol has been used for centuries in Korea and a similar version is also found in China. Around the Taegeuk you will find four symbols. Each symbol represents different things that make up the universe.
In the top left corner you can see ☰ (Geon). This symbol represents: Heaven/Sky
In the top right corner you can see ☵ (Gam). This symbol represents: Water
In the the bottom left corner you can see ☲ (Ri). This symbol represents: Fire
In the bottom right corner you can see ☷(Gon). This symbol represents: Earth
Another variant of the Taegeuk (Yin and Yang Symbol) is the Sam-Taegeuk which is made up of 3 colours, Red, Blue and Yellow. It appears in the official logo for the 1988 Olympics in Korea and you can also find it around Korea in subway stations or out on the streets. It is also painted onto a lot of supporter’s faces at sports events especially football.
A Taegeuk variant symbol is also used by Korean Air which can sometimes be confused with the Pepsi logo: