: If you believe the market is overvalued or a crash is coming, buying puts allows you to profit from that drop.
You can buy puts on the or the SPX Index . They track the same market but have different rules: SPX vs SPY: How to Trade the S&P 500 - Option Alpha buying s&p puts
: The "use-by" date. If the market doesn't drop by this time, the option expires worthless. : If you believe the market is overvalued