Diglossia

In linguistics, diglossia (/daɪˈɡlɒsiə/ dy-GLOSS-ee-ə, US also /daɪˈɡlɔːsiə/ dy-GLAW-see-ə) is a situation in which two dialects or languages are used (in fairly strict compartmentalization) by a single language community. In addition to the community's everyday or vernacular language variety (labeled "L" or "low" variety), a second, highly codified lect (labeled "H" or "high") is used in certain situations such as literature, formal education, or other specific settings, but not used normally for ordinary conversation. The H variety may have no native speakers but various degrees of fluency of the low speakers. In cases of three dialects, the term triglossia is used. When referring to two writing systems coexisting for a single language, the term digraphia is used.

The high variety may be an older stage of the same language (as in medieval Europe, where Latin (H) remained in formal use even as colloquial speech (L) diverged), an unrelated language, or a distinct yet closely related present-day dialect (as in northern India and Pakistan, where Hindustani (L) is used alongside the standard registers of Hindi (H) and Urdu (H); Hochdeutsch (H) is used alongside German dialects (L); the Arab world, where Modern Standard Arabic (H) is used alongside other varieties of Arabic (L); and China, where Standard Chinese (H) is used as the official, literary standard and local varieties of Chinese (L) are used in everyday communication). Other examples include literary Katharevousa (H) versus spoken Demotic Greek (L); Indonesian, with its bahasa baku (H) and bahasa gaul (L) forms; Standard American English (H) versus African-American Vernacular English or Hawaiian pidgin (L); and literary (H) versus spoken (L) Welsh.