The Week explores the history of the "holiday":
In the '50s, people running factories started referring to the day after Thanksgiving as "Black Friday" because so many employees failed to show up for work. In the early '60s, Philadelphia police started using the term to refer to the onslaught of jaywalking shoppers that converged on the downtown. By the '70s, the name was more widely used to connote the kick-off of holiday shopping, but still bore negative connotations. It only took on a positive ring in the '80s, when some shop owners pointed out that the profitable, big, post-Thanksgiving rush put "black ink" on their balance sheets for the first time of the year.