A mutual/linear relationship or connection between two or more things. Its values very from -1 to 1, it is of two type positive and negative correlation. or

Degree and type of relationship between any two or more variables in which they vary together over a period. or

Correlation is a statistical measurement of the relationship b/w two variables. Possible correlations range from +1 to –1. A zero correlation indicates that there is no relationship between the variables. A correlation of –1 indicates a perfect negative correlation, meaning that as one variable goes up, the other goes down. A correlation of +1 indicates a perfect positive correlation, meaning that both variables move in the same direction together.