Some communities speak one language for the news and a different one at home

Linguist Charles Ferguson coined 'diglossia' in 1959 for communities that split one language into two varieties by function: a formal 'High' form used for writing, sermons and broadcasts, and an everyday 'Low' form no one would use in a speech. Standard Arabic versus spoken Egyptian Arabic, and Swiss Standard German versus Swiss German dialect, are classic cases - and children are often not taught the High form until they start school.

— Charles A. Ferguson, Diglossia — Word, Vol. 15, No. 2, 1959