Jie Zhang, a professor of marketing at the University of Maryland’s Robert H. Smith School of Business, points to a 1951 mention of “Black Friday” in a New-York based trade publication — which noted that many workers simply called in sick the day after Thanksgiving in hopes of having a long holiday weekend.

It’s the busiest shopping week of the year, when experts say retailers will roll out their best deals on electronics, apparel, toys and more.