There is a conventional definition, courtesy of Brian Chin.
According to a Wall Street Journal article by Justin Lahart, a Minsky Moment “refers to the time when over-indebted investors are forced to sell even their solid investments to make good on their loans, sparking sharp declines in financial markets and demand for cash that can force central bankers to lend a hand.”
The Minsky Moment is the point at which a financial crisis becomes painfully obvious. It can be understood best within the context of what may be called the Minsky model of financial crises that Charles Kindleberger used in his book, Manias, Panics, and Crashes (see my earlier post on this matter).
But I also have my own definition. A Minsky Moment is the point at which you realize there are no more fools out there other than yourself. It is the end of the classic stock broker joke, when at the end of a bull run, you call him and say “Sell!” and he says “To whom?”…
A related concept is the Al Pacino Hoo-hah! moment.