An idiom is defined as - a group of words whose meaning is different from the meanings of the individual words.
Idiom:
leg work
Meaning:
routine work (that often involves walking)
Example:
I was forced to do all of the leg work to prepare for the meeting.
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.