Statistics a measure of the relationship between two variables whose values are observed at the same time; specif., the average value of the product of the two variables diminished by the product of their average values
See covariance in American Heritage Dictionary 4
(kō-vârˈē-əns)
noun
A statistical measure of the variance of two random variables that are observed or measured in the same mean time period. This measure is equal to the product of the deviations of corresponding values of the two variables from their respective means.