Herstatt risk
The risk that you have paid your side of a currency trade and your counterparty collapses before paying theirs.
The name comes from Bankhaus Herstatt in Cologne, which German regulators shut down at 3:30 in the afternoon on 26 June 1974. Its counterparties had already delivered Deutsche Marks in Frankfurt, but it was 10:30 in the morning in New York and the dollar legs had not gone out yet. They never did. Nothing was technically broken; two payment systems in different time zones simply had no idea the other existed.
The episode helped push the G10 central banks into founding the Basel Committee on Banking Supervision later that year. The practical fix took until 2002, when CLS began settling both legs at once on a payment-versus-payment basis. The risk survives for currencies and trades that don't pass through CLS, and it is still measured in trillions of dollars.