Definition - What does Flash Mob mean?
A flash mob is a brief and very sudden gathering of a large group of people who have been notified, usually on short notice, via the Internet to perform a certain action in a public setting. It most commonly ends nearly as fast as it begins and is considered an Internet trend. It is often done for entertainment and/or satire.
Techopedia explains Flash Mob
A flash mob usually gathers in an urban setting for no more than 10 minutes. The first flash mob attempt took place outside of an unassuming retail store in New York City. It originated from an email sent out by a man named Bill Wasick. In May of 2003, he sent out an email to a few dozen people instructing them to converge on a subway entrance near the store at the same time. However, the police were tipped off about the event, and put a stop to it before it could occur. Not to be discouraged, Wasik staged the first successful flash mob soon after in June 2003 at Macy's.
Over time, many Internet gags have surfaced. Just as with flash mobbing, these Internet memes are performed for the fun of it and to catch the unsuspecting public off guard.