Black Friday?

Asking my kids why the day after Thanksgiving was called Black Friday and here are a couple of the responses:

D., a ninth grader, "It's a holiday for Goths? I should know because I am one and I had a pretty good day that day."

G., a ninth grader, "A holiday for black people?"

B., an eighth grader, "Because thousands of people pack the stores and they get bruises from shoving?"