Chinese characters
In Korean, they are called hanja. Throughout most of Korean history, hanja was the only writing system most literate Koreans knew. Even though hangul was invented in 1446, it was only used by commoners and not the government until Korea gained independence from Japan. Nowadays, most Koreans write mostly in hangul. In North Korea, people write almost completely in hangul since Kim Il-sung abolished hanja from Korean. In South Korea, people mostly write in hangul, and they sometimes write hanja. Native Korean words are almost always written in hangul. Hanja are usually only used to write words that are borrowed from the Chinese language, and are usually only used when the word's meaning isn't obvious based on the context.