An idiom is a widely used saying or expression containing a figurative meaning that differs from the phrase's literal meaning.
Idiom:
like looking for a needle in a haystack
Meaning:
engaged in a hopeless search
Example:
Looking for my house keys at the beach was like looking for a needle in a haystack.
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.