“According to researchers, the name “Black Friday” dates back to Philadelphia in the mid-1960s. The Friday in question is nestled snugly between Thanksgiving and the traditional Army-Navy football game that’s played in Philadelphia on the following Saturday, so the City of Brotherly Love was always bustling with activity on that day. All of the people were great for retailers, but they were a huge pain for police officers, cab drivers, and anyone who had to negotiate the city’s streets. They started referring to the annual day of commercial bedlam as “Black Friday” to reflect how irritating it was.
Apparently storeowners didn’t love having their biggest shopping day saddled with such a negative moniker, so in the early 1980s someone began floating the accounting angle to put a more positive spin on the big day.”
via Mental Floss, “A Brief History of Black Friday“