An idiom is defined as - a group of words in a fixed order that has a particular meaning that is different from the meanings of each word on its own.
Idiom:
throw a fit
Meaning:
to become very angry
Example:
The boy's mother threw a fit when she heard about his problems at school.
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.