Standard Deviation   

Standard Deviation is a common statistical calculation that measures volatility. Other technical indicators are often calculated using standard deviations. Major highs and lows often accompany extreme volatility.
A measure of the dispersion of a set of data from its mean. The more spread apart the data is, the higher the deviation. In finance, standard deviation is applied to the annual rate of return of an investment to measure the investment’s volatility (risk).
A volatile stock would have a high standard deviation.
It is used to measure the volatility. High values of standard deviations indicate that the price or indicator is more volatile than usual