Flash is the abbreviation of "flash movie" or "flash action". It is a hippie behavior that has recently become popular all over the world. It can be regarded as a short-lived performance art. Simply put, many people use the Internet or other means to do a series of designated songs and dances or other behaviors at a designated place and time, and then leave quickly. "Flash action" is a performance art, such as pure fun or worship. Its main feature is that there is no organization and discipline, only the initiator has no organizer, and the members are all online, and they basically don't know each other.