An idiom is a group of words, or in other words, a phrase that has a meaning other than its literal meaning of the words in it.
Idiom:
stick up (someone or something) or stick (someone or something) up
Meaning:
to rob someone or something with a gun or other weapon
Example:
A man with a gun tried to stick up the small store.
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.