Black Monday

Proper noun

 * 1) Any of certain Mondays when undesirable or turbulent events have occurred.
 * 2) March 9, 2020, in the midst of the 2020 stock market crash, which resulted from market instability due to the COVID-19 pandemic. It was followed three days later by a similar event called Black Thursday.
 * 3)  The first Monday back at school after the holidays.