A flashmob is when a large group of people suddenly come together and perform some sort of action, which draws an audience very quickly. After they perform the stunt, the group of people quickly disperse.
Shay Carl, Kassem G, Lisanova, hiimrawn, mysteryguitarman, denisevlogs, and other people came together at the Planet Hollywood Resort and Casino to perform a huge flashmob. It is one of the best flashmobs on YouTube. The video is called "PHAMOUS PLANET HOLLYWOOD FLASH MOB!", uploaded on ShayCarl's channel.
A group of arts students with far too much spare time on their hands that collectively pre-arrange to "spontaneously" burst into song or theatrical performance in public spaces to annoy the general public.
I would go apeshit if a flashmob ever erupted in my presence.