Judaeo-German

Yiddish (, or , yidish/idish, lit. "Jewish", pronounced [ˈjɪdɪʃ] [ˈɪdɪʃ]; in older sources ייִדיש-טײַטש Yidish-Taitsh, lit. Judaeo-German) is the historical language of the Ashkenazi Jews. It originated during the 9th century in Central Europe, providing the nascent Ashkenazi community with an extensive Germanic based vernacular fused with elements taken from Hebrew and Aramaic, as well as from Slavic languages and traces of Romance languages. Yiddish is written with a fully vocalized alphabet based on the Hebrew script.

The earliest surviving references date from the 12th century and call the language לשון־אַשכּנז (loshn-ashknaz, "language of Ashkenaz") or טײַטש (taytsh), a variant of tiutsch, the contemporary name for Middle High German. Colloquially, the language is sometimes called מאַמע־לשון (mame-loshn, lit. "mother tongue"), distinguishing it from לשון־קדש (loshn-koydesh, "holy tongue"), meaning Hebrew. The term "Yiddish", short for "Yiddish-Teitsch" (Jewish German), did not become the most frequently used designation in the literature until the 18th century. In the late 19th and into the 20th century the language was more commonly called "Jewish", especially in non-Jewish contexts, but "Yiddish" is again the more common designation.

Modern Yiddish has two major forms. Eastern Yiddish is far more common today. It includes Southeastern (Ukrainian–Romanian), Mideastern (Polish–Galician–Eastern Hungarian), and Northeastern (Lithuanian–Belarusian) dialects. Eastern Yiddish differs from Western both by its far greater size and by the extensive inclusion of words of Slavic origin. Western Yiddish is divided into Southwestern (Swiss–Alsatian–Southern German), Midwestern (Central German), and Northwestern (Netherlandic–Northern German) dialects. Yiddish is used in a large number of Orthodox Jewish communities worldwide and is the first language of the home, school, and in many social settings among most Haredi Jews, and is used in Hasidic and Lithuanian yeshivas.