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.
Idiom:
cat burglar
Meaning:
a burglar who enters a building by climbing a wall etc.
Example:
A cat burglar entered our apartment and stole our television.
List of common idioms, their meanings and examples of their usage in sentences
An idiom is a group of words, or in other words, a phrase that has a meaning other than its literal meaning of the words in it.