What Is A Black Swan Crash? What Is A Black Swan Event?Even though black swans don't charge or roar, they nonetheless inspire anxiety and fear on Wall Street. Part of the definition of a "black swan event" is an "outlier" that has profound, far-reaching effects on investors. Throughout the history of the market, black swans have made their mark. It is the sort of "beast" that investors would do well to research and comprehend. So, what is a black swan crash?