From the link above there is this short definition, "First, it is an outlier, as it lies outside the realm of regular expectations, because nothing in the past can convincingly point to its possibility. Second, it carries an extreme 'impact'. Third, in spite of its outlier status, human nature makes us concoct explanations for its occurrence after the fact, making it explainable and predictable."
Way back in 2011 I wrote a column on this topic, see Black Swan Events Require Expanded Thinking, Planning.
If an asteroid impacts earth--that too is not a Black Swan event. We are a pocket marked planet already.