A flash mob (or flashmob) is a large group of people who assemble suddenly in a public place, perform an unusual action for a brief time, then quickly disperse. The term flash mob is generally applied only to gatherings organized via social media or viral emails. The term is generally not applied to events organized by public relations firms or as publicity stunts.
The first flash mob was created in Manhattan in May 2003, by Bill Wasik, senior editor of Harper's Magazine. The origins of the flash mobs were unknown until Wasik published an article about his creation in the March 2006 edition of Harper's. The first attempt was unsuccessful after the targeted retail store was tipped off about the plan for people to gather. Wasik avoided such problems during the second flash mob, which occurred on June 3, 2003 at Macy's department store, by sending participants to preliminary staging areas—in four prearranged Manhattan bars—where they received further instructions about the ultimate event and location just before the event began
Another example of a well known flash mob was the April 2006 silent disco in London. At various London Underground stations, people gathered with their portable music devices, and at a set time began dancing to their music. It was reported that more than 4,000 people participated at London Victoria station. This impacted the regular service of the system enough for the city's police to begin crowd control and slowly clear people. Though no one was arrested, it was reported that the City of London pledged to counter future disruption of the underground system. Since 2006, there have been several flash mobs in the London Underground, including subsequent silent discos comparable in size