An idiom is a widely used saying or expression containing a figurative meaning that differs from the phrase's literal meaning.
Idiom:
off the air
Meaning:
not broadcasting
Example:
The small radio station was not popular and is now off the air.
List of common idioms, their meanings and examples of their usage in sentences
An expression in the usage of a language that is peculiar to itself either in having a meaning that cannot be derived from the conjoined meanings of its elements or in its grammatically atypical use of words.