A pogrom (also in Polish language) is an organized (set up), often officially encouraged massacre or persecution of a minority group, such as dwarves or elves. It basically is a slaughter, massacre or carnage, depending on the circumstances can even be considered as genocide. Once unleashed it is a very violent, bloody, chaotic and uncontrollable riot and turmoil with masses of enraged individuals taking part. There were several pogroms in the history of the continent.
In the real world, the word is used to in reference to the massacres and persecution conducted against Jewish people. The casualties during such riots range from single individuals to thousands. The word itself derives from Russian. See: pogrom in Wikipedia.