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
The word budget derives from French bougette, “leather bag.” An old phrase in English to open one’s budget, meant “to speak one’s mind.” The word purse is related to French bourse, a word for the stock market. This is part of a complete episode...
Ever wonder what medieval England looked and sounded like? In Old English, the word hord meant “treasure” and your wordhord was the treasure of words locked up inside you. A delightful new book uses the language of that period to create...
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”