An idiom is defined as - a group of words whose meaning is different from the meanings of the individual words.
Idiom:
bury one's head in the sand
Meaning:
to refuse to see something, to know something unpleasant but not want to deal with it
Example:
The man always buries his head in the sand and never wants to hear about family problems.
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.