a group of people, most of whom are strangers to each other, who all unexpectedly show up at the same time in the same place, take part in some sort mellow touch of activity, and then dissipate within ten minutes of their arrival

an event where a large group of people gather at a pre-arranged spot for ten minutes and do surreal things, much to the befuddlement of passers-by

a spontaneous gathering, organised secretively by email or text message and subject to meticulous timing

Assembly of people organized as a result of Internet or mobile communication.