Have you seen the latest T-Mobile advert? The one with all the people dancing in Liverpool Street Station? This was an example of a flash mob and there may be one today in Trafalgar Square at 6pm (according to a radio station this morning).
If you don’t have any other plans, why not turn up? It could be fun!
(This was a pillow fight flash mob in Boston)
A flash mob (n.count):
a large group of people who assemble suddenly in a public place, perform an unusual action for a brief time, then quickly disperse.