A pogrom is a violent riot incited with the aim of massacring or expelling an ethnic or religious group, usually applied to attacks on Jews. The term entered the English language from Russian to describe late 19th- and early 20th-century attacks on Jews in the Russian Empire (mostly within the Pale of Settlement). Retrospectively, similar attacks against Jews which occurred in other times and places were renamed pogroms. Nowadays the word is used to describe publicly sanctioned purgative attacks against non-Jewish groups as well. The characteristics of a pogrom vary widely, depending on the specific incident, at times leading to, or culminating in, massacres.

Significant pogroms in the Russian Empire included the Odessa pogroms, Warsaw pogrom (1881), Kishinev pogrom (1903), Kiev pogrom (1905), and Białystok pogrom (1906). After the collapse of the Russian Empire in 1917, several pogroms occurred amidst the power struggles in Eastern Europe, including the Lwów pogrom (1918) and Kiev pogroms (1919). The most significant pogrom which occurred in Nazi Germany was the 1938 Kristallnacht. At least 91 Jews were killed, a further thirty thousand arrested and subsequently incarcerated in concentration camps, a thousand synagogues burned, and over seven thousand Jewish businesses destroyed or damaged. Notorious pogroms of World War II included the 1941 Farhud in Iraq, the July 1941 Iași pogrom in Romania – in which over 13,200 Jews were killed – as well as the Jedwabne pogrom in German-occupied Poland. Post-World War II pogroms included the 1945 Tripoli pogrom, the 1946 Kielce pogrom, the 1947 Aleppo pogrom, and the 1955 Istanbul pogrom.

This type of violence has also occurred to other ethnic and religious minorities. Examples include the 1984 Sikh massacre in which 3,000 Sikhs were killed and the 2002 Gujarat pogrom against Indian Muslims.

First recorded in English in 1882, the Russian word pogróm (погро́м, pronounced [pɐˈɡrom]) is derived from the common prefix po- (по-) and the verb gromít' (громи́ть, [ɡrɐˈmʲitʲ]) meaning 'to destroy, wreak havoc, demolish violently'. The noun pogrom, which has a relatively short history, is used in English and many other languages as a loanword, possibly borrowed from Yiddish (where the word takes the form פאָגראָם). Its modern widespread circulation began with the antisemitic violence in the Russian Empire in 1881–1883.

According to Encyclopædia Britannica, "the term is usually applied to attacks on Jews in the Russian Empire in the late 19th and early 20th centuries, [and] the first extensive pogroms followed the assassination of Tsar Alexander II in 1881". The Wiley-Blackwell Dictionary of Modern European History Since 1789 states that pogroms "were antisemitic disturbances that periodically occurred within the tsarist empire." However, the term is widely used to refer to many events which occurred prior to the Anti-Jewish pogroms in the Russian Empire. Historian of Russian Jewry John Klier writes in Russians, Jews, and the Pogroms of 1881–1882: "By the twentieth century, the word 'pogrom' had become a generic term in English for all forms of collective violence directed against Jews." Abramson points out that "in mainstream usage the word has come to imply an act of antisemitism", since while "Jews have not been the only group to suffer under this phenomenon ... historically Jews have been frequent victims of such violence."

The term is also used in reference to attacks on non-Jewish ethnic minorities, and accordingly, some scholars do not include antisemitism as the defining characteristic of pogroms. Reviewing the word's uses in scholarly literature, historian Werner Bergmann proposes that a pogrom should be "defined as a unilateral, nongovernmental form of collective violence that is initiated by the majority population against a largely defenseless minority ethnic group, and occurring when the majority expect the state to provide them [sic] with no assistance in overcoming a (perceived) threat from the minority". However, Bergmann adds that in Western usage, the word's "anti-Semitic overtones" have been retained. Historian David Engel supports this view, writing that while "there can be no logically or empirically compelling grounds for declaring that some particular episode does or does not merit the label [pogrom]," the majority of the incidents which are "habitually" described as pogroms took place in societies that were significantly divided by ethnicity or religion where the violence was committed by members of the higher-ranking group against members of a stereotyped lower-ranking group with which they expressed some complaint, and where the members of the higher-ranking group justified their acts of violence by claiming that the law of the land would not be used to prevent the alleged complaint.

There is no universally accepted set of characteristics which define the term pogrom. Klier writes that "when applied indiscriminately to events in Eastern Europe, the term can be misleading, the more so when it implies that 'pogroms' were regular events in the region and that they always shared common features." Use of the term pogrom to refer to events in 1918–19 in Polish cities (including the Kielce pogrom, the Pinsk massacre and the Lwów pogrom) was specifically avoided in the 1919 Morgenthau Report; the word "excesses" was employed instead because the authors argued that the use of the term "pogrom" required a situation to be antisemitic rather than political in nature, which meant that it was inapplicable to the conditions which exist in a war zone. Media use of the term pogrom to refer to the 1991 Crown Heights riot caused public controversy. In 2008, two separate attacks in the West Bank by Israeli Jewish settlers on Palestinian Arabs were characterized as pogroms by then Prime Minister of Israel Ehud Olmert.

Werner Bergmann suggests that all such incidents have a particularly unifying characteristic: "By the collective attribution of a threat, the pogrom differs from other forms of violence, such as lynchings, which are directed at individual members of a minority group, while the imbalance of power in favor of the rioters distinguishes pogroms from other forms of riots (food riots, race riots or 'communal riots' between evenly matched groups); and again, the low level of organization separates them from vigilantism, terrorism, massacre and genocide".