Q. This describes an event that comes as a surprise, has a major effect, can potentially disrupt execution of strategy
A. A black swan is an event or occurrence that deviates beyond what is normally expected of a situation and is extremely difficult to predict. Black swan events can make execution of a well crafted strategy go belly up. The term was popularized by Nassim Nicholas Taleb, a finance professor, writer and former Wall Street trader. Black swan events are typically random and are unexpected. It tries to explain, the disproportionate role of high-profile, hard-to-predict, and rare events that are beyond the realm of normal expectations in history, science, finance, and technology. Beides it highlights non-computability of the probability of the consequential rare events using scientific methods.
[Source - Internet]