The worldwide "Black Friday" is considered the biggest sale season in the US, and the world. Also, "Black Friday" is more connected to American pop culture as it came annually with the American "Thanksgiving."
After Thanksgiving, the stores open early and offer various sales. These stores are often "in the black" (profitable) that day.
"The first time the term was used applied not to holiday shopping but to the financial crisis: occurred in September 1869. Two Wall Street financiers, Jay Gould and Jim Fisk, worked together to buy up as much as they could of the nation’s gold, hoping to drive the price sky-high and sell it for astonishing profits.
On that Friday in September, the conspiracy finally unraveled, sending the stock market into free-fall and bankrupting everyone from Wall Street barons to farmers, according to History.com.
The stock market dropped 20% and foreign trade stopped. Farmers suffered a 50% dip in wheat and corn harvest value.
So, the shop owners started to exhibit discounted merchandise. The shop owners and companies used to record losses in red and profits in black when doing their accounting- from here the term came.
Another story narrated by Business Insider, in the 1950s, "Philadelphia police used the "Black Friday" term to refer to the day between Thanksgiving and the Army-Navy game. Huge crowds of shoppers and tourists went to the city that Friday, and cops had to work long hours to cover the crowds and traffic."
So the name of the day changed to be "Big Friday," but the alternative name never caught on. By the late 1980s, "Black Friday" had spread nationally with the more positive "red to black" backstory.
https://www.youtube.com/watch?v=4WjMa188Aog