colloquialism
/kəˈloʊkwiəˌlɪzəm/
noun
- A word or phrase that is used in informal, everyday conversation rather than in formal speech or writing.
- The teacher explained that 'gonna' is a colloquialism for 'going to'.
- Many colloquialisms are not appropriate for a business letter.
- 'Y'all' is a common colloquialism in the southern United States.