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VIX is a trademarked ticker symbol for the Chicago Board Options Exchange Market Volatility Index, a popular measure of the implied volatility of S&P 500 index options. Often referred to as the fear index or the fear gauge, it represents one measure of the market's expectation of stock market volatility over the next 30 day period.
The idea of a volatility index, and financial instruments based on such an index, was first developed and described by Prof. Menachem Brenner and Prof. Dan Galai in 1986. Professors Brenner and Galai published their research in the academic article "New Financial Instruments for Hedging Changes in Volatility," which appeard in the July/August 1989 issue of Financial Analysts Journal.In a subsequent paper, Professors Brenner and Galai proposed a formula to compute the volatility index.
In 1992, the CBOE retained Prof. Robert Whaley to create a stock market volatility index based on index option prices. In a January 1993 news conference, Prof. Whaley introduced and explained the index. Subsequently, the CBOE has computed VIX on a real-time basis. Based on the history of index option prices, Prof. Whaley computed daily VIX levels in a data series commencing January 1986, available on the CBOE website. Prof. Whaley's research for the CBOE appeared in the Journal of Derivatives.
The VIX is quoted in percentage points and translates, roughly, to the expected movement in the S&P 500 index over the upcoming 30-day period, which is then annualized. "VIX" is a registered trademark of the CBOE.

http://en.wikipedia.org/wiki/VIX