Definition for : Volatility
Volatility of the Value (or the Rate of return) of a Financial security characterises the amplitude of the fluctuations of this Value (or Return). Mathematically, volatility is the Variance or the Standard deviation. In a Market economy, volatility measures the Risk: the Riskier a Financial security, the higher its volatility, and vice versa.
(See Chapter 18 Risk and return of the Vernimmen)
To know more about it, look at what we have already written on this subject