Flash mob

A “flash mob” is a group of people who assemble suddenly in a public place, briefly perform or do something together, then quickly disperse. Flash mobs are often organized online on social media. A “flash mob” of online traders, or a group of online traders, sent the stock of a little-loved video game chain soaring. The online traders banded together on the social media site “Reddit” to make the stock go up. A “flash mob” of hundreds of protestors assembled to protest environmental measures.