The VIX gauges expected market volatility over the next 30 calendar days by calculating a weighted average of the implied volatilities of eight SPX calls and puts that have an average time to maturity of 30 days. Extreme high and low VIX readings can provide good contrarian signals, though it actually doesn't matter where the reading lies on an absolute basis if it is at an extreme relative to its recent readings. Buy signals often occur as the VIX reverses lower after an extreme peak, while sell signals occur as the VIX moves higher off an extreme bottom.

An index of implied volatility based on the CBOE's OEX options. The exchange calculates the implied volatility of eight at-the-money or near-the-money strikes (both puts and calls) with a weighted average time to maturity of 30 days.

The implied volatility on the S&P 100 (OEX) option. This volatility is meant to be a forward looking volatility. It is calculated from both calls and puts that are near the money. The VIX is a popular measure of market risk.

CBOE Volatility Index (symbol)

VIX is the ticker symbol for the Chicago Board Options Exchange Volatility Index, a popular measure of the implied volatility of S&P 500 index options. Referred to by some as the fear index, it represents one measure of the market's expectation of volatility over the next 30 day period.