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:
knock on wood
Meaning:
to knock on something made of wood to keep from having bad luck
Example:
I do not think that I will lose my job - knock on wood.
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.