Hasidism is a Haredi (ultra-orthodox) branch of Orthodox Judaism founded in the late 18th century in Poland. It is characterized by a dynasty of rabbis ("Rebbe" in Yiddish) who have lead the specific Hasidic movement from their home region of Eastern Europe, as well as a strict observation of the Torah and Talmud.
There are many divisions which originate from Poland, Galicia (now divided between Poland and Ukraine), and Russia, only differing slightly in some key ideological beliefs, but still keep all the characteristics of Hasidism. Some Hasidic dynasties include Chabad-Lubavitch, Zidichov, Tosh, Satmar, and Munkacs.
Hasidic Jewish men are immediately recognizable by their long side curls, beards, fedoras, and black clothing. They also have large families, which also partly account for the fast growth of Orthodox Judaism in America. Most Hasidic Jews live in New York City, in the Crown Heights, Borough Park and Williamsburg neighborhoods of Brooklyn, and in neighboring towns like Monsey and Kiryas Joel, an almost-entirely Hasidic Jewish village. There are also Hasidic populations in other major American cities. Outside of America, most Hasidic Jews live in Jerusalem.
Their main language is Yiddish, though in America they speak English as well. In Israel, they speak Hebrew as their everyday language, though some Hasidim oppose the use of Hebrew as an everyday language and speak Yiddish instead.