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.
Idiom:
drop (someone) a line
Meaning:
to write or mail a note or letter to someone
Example:
My friend promised that she will drop me a line when she gets to Singapore.
List of common idioms, their meanings and examples of their usage in sentences
An idiom is a widely used saying or expression containing a figurative meaning that differs from the phrase's literal meaning.