A strange phenomenon wherein a group of people plans a secret event to take place at a public location. The planning usually occurs online. Flash parties are usually silly, fun affairs.

All of a sudden a small group of people become intoxicated, dance, then sober up and leave within a few hours.

A social gathering on an "off night" of the week, usually at a bar or someone's house/apt, that starts out small but suddenly, unintentionally, and randomly reaches critical mass and turns into drunken mayhem.