An idiom is a type of phrase or expression that has a meaning that can't be deciphered by defining the individual words.
Idiom:
talk shop
Meaning:
to talk about things related to one`s work
Example:
Everybody at the company gathering agreed not to talk shop during the dinner.
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.