An idiom is a type of phrase or expression that has a meaning that can't be deciphered by defining the individual words.
Idiom:
burn a hole in one's pocket
Meaning:
to stimulate someone to spend money quickly
Example:
I got paid today and the money is burning a hole in my pocket.
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.