해라체 (haerache) is a speech level used with close friends, relatives of similar age, or younger people. It is also used almost universally in books, newspapers, and magazines; also used in reported speech ("She said that...").
Korean words inflected in this speech level are characterized by the ending ㄴ다 present tense, ㅆ다 in the past tense, and 라 in the imperative. E.g.: