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
Twice a day the River Thames recedes, revealing a muddy shoreline. Hobbyists known as mudlarks stroll the surface searching for objects that have found their way into the river over the centuries, everything from ancient Roman jewelry to modern...
Astronauts returning from space say they experience what’s called the overview effect, a new understanding of the fragility of our planet and our need to reflect on what humans all share as a species. A book about the end of the universe...
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”