Colloquialism
Part of speech: noun
Definition: A colloquial word or phrase; a common spoken expression, often regional.
Idiom
Part of speech: noun
Definition: A manner of speaking, a way of expressing oneself.An artistic style (for example, in art, architecture, or music); an instance of such a style.A locution peculiar of a particular language, that cannot be understood by way of a literal translation.A communicative system under study, which could be called either a dialect or a language, when its status as a language or dialect is irrelevant.A programming technique which experienced programmers in a language are assumed to know.