Hanja is the name for Chinese characters used in the Korean language. It is believed that approximately 70% of Korean vocabulary comes from Hanja. Grammar in the Korean language is completely different to that found in Chinese, however, the effect of the Chinese on its neighbouring countries has been strong, and this can be seen in the usage of Hanja. Korean was once written entirely in Hanja until the invention of the Hangeul script by King Sejong and his scribes, even then Hanja was mainly used until the end of World War II.
Hanja, though not used as often as before, is often used in important documents where precision is required. It is almost entirely identical to the characters used in traditional Chinese. Japan also uses its version of Hanja, called Kanji, however they tend to use a more simplified version. Most compounded Hanja mean the same thing in Japanese.