Black Monday was October 28, 1929, when the Dow Jones Industrial Average fell about 13 percent during the Wall Street Crash.
The decline came after the market had already suffered severe losses on Black Thursday. Investors faced increasing pressure to provide cash for purchases made with borrowed money, and forced selling added to the downward momentum.
Black Monday is commonly mixed up with Black Tuesday, October 29, when the Dow fell even farther in a record-volume session. Black Thursday, October 24, marks the earlier panic, while the three names describe separate trading days.
The crash reflected speculative excesses that had built during the 1920s. Margin trading, optimistic forecasts, and high valuations made the market vulnerable when confidence weakened. The crash itself did not single-handedly cause the Great Depression, but it intensified financial and economic distress.