The VIX is a measure of the implied or expected volatility of S&P 500 options over the next 30 days. Implied volatility is the market’s estimated future volatility and is reflected in the premiums paid for options.
Originally launched in 1993, the VIX underwent a change in calculation in September 2003. The “original” VIX was calculated using at-the-money put and call options on the S&P 100 index OEX. Furthermore, the original VIX was based on prices of only eight at-the-money OEX puts and calls, the most actively traded index options at the time.