The variance of a variable is a measure of how far the values tend to be from the sample mean. When all the values are close to the mean, the variance is small (but never less than 0). When the values are widely scattered about the mean, the variance is larger. The variance is 0 only if all the values are the same.
Computationally, the variance is the sum of the squared deviations from the mean, divided by the number of values minus 1.
The square root of the variance is the standard deviation.
At least two nonmissing values are required for computing the variance.