An idiom is a group of words, or in other words, a phrase that has a meaning other than its literal meaning of the words in it.
cheek by jowl
side by side, in close intimacy
The fans entered the stadium cheek by jowl.
List of common idioms, their meanings and examples of their usage in sentences
An idiom is defined as - a group of words in a fixed order that has a particular meaning that is different from the meanings of each word on its own.