An idiom (full name is idiomatic expression) can be an expression, word, or phrase that only has a meaning to the native speaker. The meaning of an idiom is total different from the literal meaning of the idiom's individual elements. Idioms do not mean exactly what the words say. They have a hidden meaning. Of course, we also use the word phrase to refer to a short group of words that have a particular meaning when they are used together, such as rain cats and dogs, play for time, or a square meal.
