Economically speaking today is “The Day” for many retailers to take in massive amounts of revenue from eager holiday shoppers. “Black Friday” has been embedded into the American culture for many decades now. The term itself is hardly ever explored in its origin. I have found one historical explanation via The American Dialect Society:

[From *Public Relations News*, 18 December 1961, p. 2. This weekly
newsletter was published by Denny Griswold of 815 Park Avenue, New
York, NY.]

Santa has brought Philadelphia stores a present in the form of “one of
the biggest shopping weekends in recent history.” At the same time,
it has again been proven that there is a direct relationship between
sales and public relations.

For downtown merchants throughout the nation, the biggest shopping
days normally are the two following Thanksgiving Day. Resulting
traffic jams are an irksome problem to the police and, in
Philadelphia, it became customary for officers to refer to the
post-Thanksgiving days as Black Friday and Black Saturday. Hardly a
stimulus for good business, the problem was discussed by the merchants
with their Deputy City Representative, Abe S. Rosen, one of the
country’s most experienced municipal PR executives. He recommended
adoption of a positive approach which would convert Black Friday and
Black Saturday to Big Friday and Big Saturday. The media cooperated
in spreading the news of the beauty of Christmas-decorated downtown
Philadelphia, the popularity of a “family-day outing” to the
department stores during the Thanksgiving weekend, the increased
parking facilities, and the use of additional police officers for
guaranteeing a free flow of traffic … Rosen reports that business
over the weekend was so good that merchants are giving downtown
Philadelphia “a starry-eyed new look.”