Volatility
 
​As explained in the definition for standard deviation, volatility refers to the amount of uncertainty or risk about the size of changes in a security's value.  A higher volatility means that a security's value can potentially be spread out over a larger range of values.  This means that the price of the security can change dramatically over a short time period in either direction.  A lower volatility means that a security's value does not fluctuate dramatically, but changes in value at a steady pace over a period of time.
 
Mathematically, volatility is the standard deviation annualized in percentage terms.