Definition of flash mob in US English:

flash mob

noun

  • A large public gathering at which people perform an unusual or seemingly random act and then disperse, typically organized by means of the Internet or social media.

    ‘equipped with cameras and LED lights, a flash mob of 135 people appeared out of nowhere to put on a performance’

Pronunciation

flash mob

/ˈflæʃ ˌmɑb//ˈflaSH ˌmäb/