An idiom is defined as - a group of words whose meaning is different from the meanings of the individual words.
cry over spilt milk
to cry or complain about something that has already happened
"Don`t cry over spilt milk. You can never change the past."
List of common idioms, their meanings and examples of their usage in sentences
An idiom is a type of phrase or expression that has a meaning that can't be deciphered by defining the individual words.