Wikipedia's quote: "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 quiclky disperse.
The term flash mob is generally applied only to gatherings organized via telecommunications, social media or viral emails."
Oprah Winfrey's programm is live on TV for its 24th season (2009-10). For the official opening, the Black Eyed Peas perfomed their hit "I Gotta Feeling" for 21,000 fans on Michigan Av. in Chicago. As it looks like at the video, Oprah didn't knew in advance that all the fans suddenly started one flash mob dance... Enjoy it!