'Black Friday' definitions:

Definition of 'Black Friday'

From: GCIDE

Black Friday \Black Friday\ Any Friday on which a public disaster has occurred, as: In England, December 6, 1745, when the news of the landing of the Pretender reached London, or May 11, 1866, when a financial panic commenced. In the United States, September
24, 1869, and September 18, 1873, on which financial panics began, and especially October 29, 1929, when a dramatic drop in stock prices contributed to the factors which began the great depression of the 1930's. [Webster 1913 Suppl. +PJC]
The last week of October 1929 remains forever imprinted in the American memory. It was, of course, the week of the Great Crash, the stock market collapse that signaled the collapse of the world economy and the Great Depression of the 1930s. From an all-time high of 381 in early September 1929, the Dow Jones Industrial Average drifted down to a level of 326 on October 22, then, in a series of traumatic selling waves, to 230 in the course of the following six trading days. The stock market�s drop was far from over; it continued its sickening slide for nearly three more years, reaching an ultimate low of 41 in July 1932. But it was that last week of October 1929 that burned itself into the American consciousness. After a decade of unprecedented boom and prosperity, there suddenly was panic, fear, a yawning gap in the American fabric. The party was over. --Wall street Journal, October 28, 1977 [PJC]