It is the measure of the degree of relationship between the variables, i.e. the degree of their relatedness. It varies from +1 to -1.
0 to -1 would mean negatively correlated. I.e. an increase in one variable would cause decrease in another variable and vice versa.
0 to +1 would mean positively correlated. I.e. an increase in one variable would cause increase in another variable and vice versa.
Example: There’s a positive correlation between studying and marks obtained in the exam.
The Carl Pearson’s coefficient of variation is defined as follows.
Where x and y are two variables.