A stock market index is a measurement of a portion of the stock market. It is calculated from the prices of selected stocks (often a weighted average). It is a tool used by financial managers and investors to describe the market, and to compare the return on specific investments. Below you will find an interactive chart of the CBOE Volatility Index (VIX), which measures the market's expectation of 30-day volatility based on S&P 500 index options. The VIX is often referred to as the market's "fear gauge."
