Korea, officially the Republic of Korea (lit. The Nation of Great Han; ROK), is a sovereign state in East Asia. The name Korea is derived from the ancient Kingdom of Goguryeo, also known as Koryŏ. It shares borders with Japan to the east and China to the north and to the west. Roughly half of the country's 51 million people reside in the Seoul Capital Area, the second largest in the world with over 25 million residents.