What is the essential difference between correlation and covariance?

The correlation is a coefficient that indicates the strength and direction of a linear relationship between two random variables.

This coefficient is computed as the quotient between the covariance of these two randon variables and the square root of the product of their variances. So if r(X,Y) is the correlation of X and Y and COV(X,Y) is the covariance then:

r(X,Y)=COV(X,Y)/sqrt(COV(X,X)*COV(Y,Y))

Covariance and correlation are related parameters that indicate the extent to which two random variables co-vary. Correlation is a scaled version of covariance