A put option is a financial contract that gives the holder the right to sell an asset at a specific price by (or at) a specific date. A put option can therefore provide its holder insurance against a large drop in the stock price. This makes the prices of put options an ideal source of information for a market-based measure of the probability of a firm’s default.
This equilibrium model explains the trend in long-term yields and business-cycle movements in short-term yields and yield spreads. The less-frequent inverted yield curves (and less-frequent recessions) after the 1990s are due to recent secular stagnation and procyclical inflation expectations.