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:
have one's heart in the right place
Meaning:
to have good intentions (even if the results may be bad)
Example:
The woman has her heart in the right place and is always ready to help if she can.
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.