By ancient superstition Friday is an ill-omened day.
Black Friday (plural Black Fridays)
- A Friday falling on the 13th day of the month (and therefore doubly ill-omened).
- Any Friday actually darkened by catastrophe.
- The anniversary of a number of catastrophic or unfortunate historical events originally occurring on a Friday.
- (obsolete?) Good Friday
Because retailers typically post profits ('in the black') rather than losses ('in the red').
- (US, business, retailing) The day after Thanksgiving Day, generally regarded as the first day of the Christmas season, and the busiest shopping day of the year. (Although this usage may also very possibly originate in Etymology 1)
- by extension, the sales period involving heavy price reductions immediately following U.S. Thanksgiving Day, from Friday (the original Black Friday) through Monday (Cyber Monday).
day after U.S. Thanksgiving Day