It refers to the day after Thanksgiving (Friday) and it's called "Black" because hopefully all the sales going on will put the retailers "In the Black" financially, so to speak.
The term "Black Friday" originated in Philadelphia in the mid 1960's. (by some woman)
It refers to the Friday after Thanksgiving as be the busiest (Christmas) shopping day of the year in the U.S., therefore giving retailers a profit and putting them in the "black".
Thank you for that information. I've never heard it before.
The retailers are in the "black" (making profit) vs. the "red" (losing money) I think.