anil dash: "Flash Mobs are striking in that they are an affinity event for people who have no affinity group. A Meetup for people who like Meetups. How much more meta can it get? None. None more meta".

for further definitions refer to anil dash's daily links ("meetup for white people who don't have any hobbies") and the devil's dictionary ("an impromptu gathering, organized by means of wireless communication, of the unemployed").