Covariance is a statistical measure of the joint variability of two random variables. It is used to determine the relationship between the movements of two variables. Covariance measures how much two variables change together, and it is calculated by multiplying the deviations of the two variables from their respective means. A positive covariance means that the two variables tend to move in the same direction, while a negative covariance means that they tend to move in opposite directions. Covariance is related to variance, which measures the spread of data along a single axis, while covariance examines the directional relationship between two variables. Covariance is used in various fields, including finance, meteorology, and oceanography.