In the term Black Friday, black means marked by misfortune or disaster.
The Friday after Thanksgiving was first referred to as Black Friday by factory managers in the 1950s when workers would call in sick in order to extend their holiday weekend.
10 years later, in the 1960s, the term Black Friday was used again,  this time by traffic cops in Philadelphia. That’s because they were required to work 12-hour shifts in terrible traffic on the day after Thanksgiving.
Later in the 1980s when the terms in the black and in the red were coined in the business world, we started calling the busiest shopping day of the year – the day after Thanksgiving – Black Friday.