Long Term Capital Management (LTCM)
This was a hedge fund founded in 1994. It performed well initially, but had a catastrophic year in 1998, losing almost $5 billion.
It was an early example of a potential financial contagion that threatened to cascade through the markets, so it was bailed out by a consortium of banks organized by the Federal Reserve.
The final resolution split ownership of LTCM among multiple institutions, and it was eventually liquidated in the early 2000s. The crisis derailed the careers of multiple prominent people in the financial world.
Why I Looked It Up
I had heard the term sporadically over the years, but it came up repeatedly in a book about the history of capital markets.