The Volatility Index (VIX) measures expectations for volatility in the next 30 sessions, with put and call options activity underlying its calculations.
Volatility represents the magnitude of the price change in a security, such as a stock or commodity.
The CBOE VIX shows the market's expectations for near-term price changes in the S&P 500 index (SPX).
The VIX represents the expectation that volatility will rise or fall, which is why it's often called the fear index.
As a result, price moves in the S&P 500 and equity markets are inversely correlated to price changes in the VIX.