flash mob

a large group of people organized using social media who gather together publicly at an exact time, do something for a short time and then disperse

A flash mob is a group of people who gather suddenly in a public place to perform a planned activity, such as a dance or a song, before quickly dispersing. These events are usually organized through social media or online messaging, and they are often done for entertainment, awareness, or as a form of artistic expression. Flash mobs are meant to surprise and engage onlookers, creating a sense of excitement and spontaneity. They can range from simple performances to more elaborate and creative displays, and are typically short in duration.