Standard Deviation
Definition
A measure of the dispersion or spread of values in a data set around the mean. It is the square root of Variance. A lower standard deviation indicates data points are clustered close to the mean; a higher value indicates greater spread.
Example
"If the returns on a mutual fund over 5 years are 8%, 10%, 7%, 12%, 8%, the standard deviation quantifies how much these returns deviate from the average return of 9%."