Idiom is a phrase or expression whose total meaning differs from the meaning of the individual words. For example, to blow one's top (get angry) and behind the eight ball (in trouble) are English- language idioms. Idioms come from language and generally cannot be translated literally. Foreign language speakers must learn them just as they would learn vocabulary words. This article defines idioms, phraseological units and formulaic expressions. Moreover, usage of them and examples were given in this paper.