An idiom is a phrase (a group of words) whose meaning is different than each of the words considered separately.
Idioms are a type of figurative language that can be used to add dynamism and character to otherwise stale writing. You can also use idioms to Express Complex Ideas in a Simple Way. Oftentimes, idioms can help express a large or abstract idea in a way that is succinct and easy to understand.
Idioms are phrases whose meanings cannot easily be known from the meanings of each word in the phrase. While idioms are quite transparent to native speakers of a language, they are a source of frustration and perplexity for those seeking to learn a new one.