Definition of 'Variability'
The extent to which data points in a statistical distribution or data set diverge from the average or mean value. Variability also refers to the extent to which these data points differ from each other. There are four commonly used measures of variability: range, mean, variance and standard deviation.
The risk perception of an asset class is directly proportional to the variability of its returns. As a result, the risk premium that investors demand to invest in assets, such as stocks and commodities, is higher than the risk premium for assets such as Treasury bills, which have much lower return variability.
Investopedia explains 'Variability'
Variability is used to standardize the returns obtained on an investment. One measure of reward-to-variability is the Sharpe ratio, which measures the excess return or risk premium per unit of risk for an asset. All else being equal, the asset with the higher Sharpe ratio delivers more return for the same amount of risk.