An idiom is a widely used saying or expression containing a figurative meaning that differs from the phrase's literal meaning.
to fall asleep quickly and with great fatigue
After we returned from the hike, I immediately conked out in front of the TV.
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.