Klezmer (Yiddish כליזמר or קלעזמער, pl כליזמר,כליזמרים, from Hebrew כלי זמר — instruments of music) is a musical tradition of the Ashkenazic Jews of Eastern Europe. Played by professional musicians called klezmorim, the genre originally consisted largely of dance tunes and instrumental display pieces for weddings and other celebrations. The genre has its origins in Eastern Europe. In the United States the genre morphed considerably as Yiddish-speaking Jewish immigrants from Eastern Europe, who arrived between 1880 and 1924, met and assimilated American jazz.
During the initial decades after the “Klezmer Revival,” this was what most people knew as klezmer, although in the current century musicians have begun paying attention to the “original” pre-jazz traditions as some original revivialists (e.g., Josh Horowitz, Yale Strom, Bob Cohen) spent years doing field research in Eastern/Central Europe. Additionally, late immigrants from the Soviet Union such as German Goldenshtayn brought their surviving repertoires to the United States and Israel in the 1980s.(with thanks to wikipedia)