An idiom is an expression that takes on a figurative meaning when certain words are combined, which is different from the literal definition of the individual words.
An idiom is a phrase, or a combination of words, that has developed a figurative meaning through frequency of use. Idioms are a staple in many different languages, and are often shared across languages through numerous translations. They can be useful and even fun to use, but are also bound to confuse any new speaker of a language who isn’t familiar with the phrase’s cultural relevance.