A group of words which have a different meaning when used together from the one they would have if you took the meaning of each word separately.
Idiom:
hide one's head in the sand
Meaning:
to refuse to see something, to know something but not want to deal with it
Example:
The employee hates to talk about important matters and hides his head in the sand when I try to talk to him.
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.