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.
over and over
repeated many times
I told my friend over and over that I do not want to go to a movie.
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.