In The UK, September 16, 1992, is known as Black Wednesday, the day when speculators including George Soros and Stanley Druckenmiller "broke the pound."
This expression is used to describe the moment in time where market forces coalesced to force the British government to exit the European Exchange Rate Mechanism (ERM) by removing its currency from that agreement.
Joining the ERM was part of Britain's effort participate in a single European Currency.