Diglossia is a situation where a language that has two forms, one a ‘higher' and more prestigious form used by educated speakers in formal situations, and the other a ‘lower', vernacular form used more commonly. Although English is not a diglossic language, it does have a wide variety of dialects, colloquial forms and levels of formality.
Greek, Arabic and Tamil are diglossic languages.
In the classroom
Teachers working with multi-lingual groups may find this is an interesting area to explore if there are learners in the class who speak diglossic languages. Learners can explain the different types of language and the roles they have in society and comparisons can be made with English.