Volatility is a statistical measure of the dispersion of returns for a given security or market index. Volatility can either be measured by using the standard deviation or variance between returns from that same security or market index. Commonly, the higher the volatility, the riskier the security.What does it mean "commonly"? As for me, volatility is risky only for the investor that is forced to cash its share at a certain date. If the investor is free to wait out the low cycle (the price tends to regress to the mean, doesn't everything?) and he has patience - sigma is no risk at all.