Wall Street Crash

The  occurred in October 1929 in the United States of America. After enjoying a period of "wealth and excess" throughout the 1920s, the stock market suddenly suffered the worst crash in its history, leading to the Great Depression. The impact of the Crash was felt across the globe, with particularly notable effects on the United Kingdom and Germany. The Depression lasted ten years until the Second World War brought it to an end. (PROSE: A History of Humankind)

Peri Brown named it when the Sixth Doctor tried to remember something important that happened in 1929. (PROSE: Timeshare)