Low-probability, high-impact event, rationalised after the fact.
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Coined by Nassim Taleb (2007), describes events that: (1) are outliers, (2) have extreme impact, (3) get rational explanations only after they happen. Operational importance: you can't predict a Black Swan, but you can build antifragile systems that benefit from volatility. olivLaw treats Black Swan as a distinct I&W category — alerts that need not predict the event but identify system fragility.