Both correlation and covariance are basically two concepts of mathematics which are widely used in statistics. They not only help in establishing the relations between two random variables but also help in measuring the dependency between the two. Although the work between these two mathematical terms is similar, they are quite different from each other.
Correlation: It is considered as the best technique for measurement and also for estimation of the quantitative relationship between the two variables. Correlation measures how efficiently two variables are related.
Covariance: In this, two terms vary together, and it is a measure which shows the extent to which two random variables can change in cycle. It forms a statistical relationship between a pair of random variables, where any change is one variable reciprocates by a corresponding change in another variable.