flash mob
noun/ˈflæʃ mɒb/
/ˈflæʃ mɑːb/
- a large group of people who arrange (by mobile phone or email) to gather together in a public place at exactly the same time, spend a short time doing something there and then quickly all leave at the same time
快闪族（通过手机或电邮相约同一时间在公共场所速聚速散的一大群人）