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From the Holocaust Encyclopaedia:
Pogrom is a Russian word meaning “to wreak havoc, to demolish violently.” Historically, the term refers to violent attacks by local non-Jewish populations on Jews in the Russian Empire and in other countries. The first such incident to be labeled a pogrom View This Term in the Glossary is believed to be anti-Jewish rioting in Odessa in 1821. As a descriptive term, “pogrom” came into common usage with extensive anti-Jewish riots that swept the southern and western provinces of the Russian Empire in 1881–1884, following the assassination of Tsar Alexander II.
The perpetrators of pogroms organized locally, sometimes with government and police encouragement. They raped and murdered their Jewish victims and looted their property. During the civil war that followed the 1917 Bolshevik Revolution, Ukrainian nationalists, Polish officials, and Red Army View This Term in the Glossary soldiers all engaged in pogrom-like violence in western Belorussia (Belarus) and Poland's Galicia province (now West Ukraine), killing tens of thousands of Jews between 1918 and 1920.