diglossia

/daɪˈɡlɒsiə/
noun
  1. A situation in which two distinct varieties of a language are used within a community, one for formal or written contexts and another for everyday conversation.
    • In many Arabic-speaking countries, diglossia means people use Classical Arabic for writing and news but a local dialect for casual talk.
    • Diglossia is common in Switzerland, where Standard German is used in schools and Swiss German is spoken at home.
    • The study of diglossia helps linguists understand how languages change and split over time.