black swan event
n.— «On Black Monday, October 19, 1987, the Dow Jones index, for reasons still being debated, fell 508 points, almost a quarter of its total. (The current equivalent, for comparison’s sake, would be a 3,200-point loss on one day.) The drop turned out to be a “black swan event,” a weirdly poetic economist’s term meaning, basically, a fluke (though few people remember it, the Dow still eked out a positive finish for the year).» —“The Stench of ‘89″ by Michael Idov New York Magazine (New York City) Feb. 4, 2008. (source: Double-Tongued Dictionary)
Further reading
In 1971, when a new public library opened in Troy, Michigan, famous authors and artists were invited to write letters to the city’s youngest readers, extolling the many benefits of libraries. One of the loveliest was from E.B. White, author of...
Michael from Jones, Michigan, says he was stationed on a U.S. Army base in Germany in the early 1960s. If there was a gust of cold wind, a fellow soldier would say the hawk’s out. This expression is largely associated with Chicago, Illinois...
I believe Nassim Taleb coined this term in his book “Fooled by Randomness: The Hidden Role of Chance in Life and the Markets”, and then explored it further in “The Black Swan: The Impact of the Highly Improbable”