Grey swan https://www.investopedia.com/terms/g/grey-swan.asp
Black swan https://www.investopedia.com/terms/b/blackswan.asp
https://accendoreliability.com/black-swans-grey-swans-white-swans/
Grey Rhino https://www.fastcompany.com/90475793/why-the-coronavirus-crisis-is-a-gray-rhino-and-not-a-black-swan
Leadingchurch.com 