The earliest evidence of the phrase Black Friday applied to the day after Thanksgiving in a shopping context suggests that the term originated in Philadelphia, where it was used to describe the heavy and disruptive pedestrian and vehicle traffic that would occur on the day after Thanksgiving. This usage dates to at least 1961. More than twenty years later, as the phrase became more widespread, a popular explanation became that this day represented the point in the year when retailers begin to turn a profit, thus going from being "in the red '' to being "in the black ''.
why they call the day after thanksgiving black friday
to describe the heavy and disruptive pedestrian and vehicle traffic that would occur