A smart mob is a group whose coordination and communication abilities have been empowered by digital communication technologies. Smart mobs are particularly known for their ability to mobilize quickly.
Smart mob on occasion of United Nations 'Children's Day'. Vienna, Austria, in 2010-11-20.
A flash mob is a group of people that assembles suddenly in a public place, performs for a brief time, then quickly disperses, often for the purposes of entertainment, satire, and/or artistic expression. Flash mobs may be organized via telecommunications, social media, or viral emails.
A public pillow fight in Bologna, Italy
Flash mobbing was quickly imitated outside of the United States. This picture is of "sydmob" 2003, the first flash mob held in Sydney, Australia.
People dancing at the Eutopia 15 Flashmob Event while crossing Puerta del Puente in Córdoba, Spain (2015)