Definition Colloquial term for any extremely rare event. The term was popularized by a book by Nassim Nicholas Taleb, entitled "The Black Swan", and was based on a previous belief (now a mis [..]

Black swan is a term coined by Nassim Nicholas Taleb, used to describe unforeseen events in business that change previous thinking (based on the old Western belief that swans must be white before the [..]

(See RARA AVIS.)

A market event that is completely unpredictable and often without historical precedent. The sell-off on 2/27/07 would be considered a “black swan” event. By the same token the advance that followed it within three weeks pushing the market quickly back over the highs of 2/27 and much further could also be characterized this way.

An occurrence believed impossible or not to exist, subsequently shown to exist. An Australian swan whose feathers are black. An occurrence believed impossible or not to exist.

lang=en *title=, Ratiocinative and Inductive|page=379|author=|year=1843|passage=As there were black swans, though civilised people had existed for three thousand years on the earth without meeting wi [..]